Reversible aminal gel compositions, methods, and use

ABSTRACT

A well treatment composition for use in a hydrocarbon-bearing reservoir, optionally as a kill pill, and comprising a reversible aminal gel composition. The reversible aminal gel composition includes a liquid precursor composition. The liquid precursor composition is operable to remain in a liquid state at about room temperature. The liquid precursor composition comprises an organic amine composition; an aldehyde composition; a polar aprotic organic solvent; and a metal salt composition. The liquid precursor composition transitions from the liquid state to a gel state responsive to an increase in temperature in the hydrocarbon-bearing reservoir. The gel state is stable in the hydrocarbon-bearing reservoir at a temperature similar to a temperature of the hydrocarbon-bearing reservoir, and the gel state is operable to return to the liquid state responsive to a change in the hydrocarbon-bearing reservoir selected from the group consisting of: a decrease in pH in the hydrocarbon-bearing reservoir and an addition of excess metal salt composition in the hydrocarbon-bearing reservoir.

PRIORITY

The present application is a continuation-in-part application of andclaims priority to and the benefit of U.S. patent application Ser. No.15/864,694, filed Jan. 8, 2018, which itself is a continuationapplication of and claims priority to and the benefit of U.S. patentapplication Ser. No. 15/423,765, filed on Feb. 3, 2017, and now issuedas U.S. Pat. No. 9,879,170, which claims priority to and the benefit ofU.S. Prov. Pat. App. Ser. No. 62/290,713, filed Feb. 3, 2016, the entiredisclosures of which are expressly incorporated here by reference.

BACKGROUND Field

Embodiments of the disclosure relate to oil and gas recovery. Inparticular, embodiments of the disclosure relate to gel compositionsuseful in downhole applications.

Description of the Related Art

Hemiaminal and aminal polymers have been reported to undergo pHresponsive phase change and network rearrangements giving them promiseas recyclable plastics, self-healing polymers, and stimulus-responsivematerials. In addition to pH responsiveness, hemiaminal gels also showdynamics through aminal/thiol-exchange.

Constitutionally dynamic materials (CDMs) are classified by theirutilization of reversible covalent in addition to or alternative tonon-covalent bonding such that they are able to undergo modifications totheir constitutions through the dissociation and re-association of theirconstituent building blocks. This attribute helps allow for accessingtriggered release, reversible gels, and self-healing composites. Themonomeric units of CDMs are brought together through reversiblemolecular bonding or supramolecular bonding (which is inherentlyreversible).

CDMs generated by the reversible covalent association of organic andorganometallic building blocks are marked by stronger bonding than theirsupramolecular counterparts and have the additional flexibility ofaccess to a greater variety of dynamic chemical reactions. An assortmentof different reversible reactions has been investigated in this class ofmaterials. These include reversible hydrazone formation, reversibleSchiff base formation, reversible aminal formation, Diels-Aldercondensations, disulfide exchange, dithioacetal exchange, dynamicboronic ester formation, olefin metathesis, and metal-ligandassociation.

Both constitutional and motional covalent dynamic chemistries have beendemonstrated through reversible imine formation and the transformationof imines into aminals. Experiments have demonstrated that thecomplexation of certain transition metals to condensation products ofpolyamines and aldehydes can result in a switch from the aminalcondensation product to the Schiff base. The transformative potential ofcertain metals in the presence of aminals could permit for networkedpolymers endowed with uniquely dynamic rheological and dielectricproperties. These properties are of certain utility in the drilling,construction, and remediation of oil and gas producing wells.

In oil field services, completion fluids can be defined as those fluidsused to flush potentially formation damaging materials from the wellboreafter drilling and before casing perforation. Damaging materials includedrilling fluid additives, such as fluid loss agents, on the formationface, solid cuttings and clays from formations entrained in the drillingfluid and deposited on the face of a formation, and filter cake on theformation left from the drilling fluid. The filter cake typicallycontains solid materials from drilling fluid additive residue from thedrilling fluid along with the filter base (depending on the oil or waterbase of the fluid). Completion fluids control well pressure, prevent thecollapse of tubing from overpressure, and provide fluid loss control.Fluid loss control agents can be added to the bulk completion fluid orsupplied as a pill. Typical fluid loss pills are oil-soluble resins,calcium carbonate, and ground salt. These material are known to causeformation damage, which can significantly reduce production levels bydecreasing the permeability of formations.

Gravel packing is used to control sand migration from the formation intothe wellbore in both open hole and perforated casing situations. In thecase of casing gravel pack completion, it is inserted at a specifiedlocation within a perforated wellbore. Conventional gravel packing usesa fine sand or gravel in a fluid viscosified or gelled with a polymersuch as uncrosslinked hydroxyethyl cellulose, hydroxypropyl guar,xanthan gum, or similar. The thickener thickens or gels the fluid toallow the sand to pack the perforations before it compacts. Afterpacking, the fluids or gels are then thinned or broken and recovered inorder to allow the settlement of the sand to properly pack the annulus.The gels are converted to fluids by breakers, which are often chemicalagents.

The gravel pack that remains is designed to be highly permeable but alsoblocks any formation sand from passing into the wellbore and only allowsfor the passage of fluids. If a thickening agent is not used or if itthins too early the result can be premature ‘sand-out’, which is causedby bridging of the settled particles across the tubing. A viscosifiedfluid or gel with an infinite gravel settling rate is required in highlydeviated wells. This assures that the gravel carried to the productionzone in a highly deviated wellbore will not settle out. Cellulosederivatives are preferred viscosifiers as they render only a limitedamount of water insoluble particles or residues when they degrade. Thesepolymers are known to degrade at temperatures exceeding 200° F.Therefore, effective reversible thickeners and gelling agents are ofcertain utility in well sections exceeding 200° F.

Workover fluids are typically used in cleaning and repairing old wellsto increase production. Completion, workover, and kill fluids aretypically designed to prevent fluid from the formation intrusion intothe wellbore while preventing wellbore fluid leakoff. Leakoff is theloss of fluid from the wellbore into the formation. Fluid leakoff isknown to cause formation damage, which can potentially reducehydrocarbon recovery. Formation damage can be manifested as reducedpermeability of the formation or the reaction of an aqueous fluid withminerals, such as clays, in the formation.

During perforation, it is necessary to inhibit fluids from entering anddamaging the formation. Fluid loss agents typically used to meet theseends are water insoluble, oil soluble waxes, soaps, gels, and variousother types of polymers. Another type of treatment fluid is comprised offinely ground solids dispersed in a fluid. The solids can be guar-coatedsilica flour, crushed oyster shells, crushed limestone, or rock salt.

To prevent fluid leakoff, lost circulation materials are often added towellbore construction fluids. These additives are designed with thepurpose of preventing the communication of wellbore fluids with theformation. Conventional lost circulation materials may be inapplicableto water sensitive formations or formations with low fracture gradients.Cross-linked polymer gels have shown certain advantages overconventional completion, kill, and workover fluid additives because oftheir enhanced fluid loss control in high permeability formations. Thedifficulty with many gels is that formation damage can be caused by thegels as they are often difficult to remove. If the gels are made fullyreversible with an effective gel breaker, this formation damage issuemay no longer be problematic in the use of gels in these kinds offluids.

Problems in drilling and completion practices include well blowoutscaused by the escape of hydrogen sulfide (H₂S), other gases, and lighthydrocarbons. These events lead to serious costs and safety hazards tofield personnel and well operators. The conventional method to mitigateH₂S-related events is to disperse solid particles such as iron oxide orzinc carbonate in aqueous brine weighted fluids to react with H₂S. Thedifficulty with this practice is that the brines are no longer free ofsolids as their intended purpose would be so as to avoid potentialformation damage. Non-aqueous fluids, such as N-methyl pyrrolidone(NMP), are known to have a high capacity for H₂S absorption. Fluidsbased with NMP have been previously proposed for use in wells with H₂Sto minimize well blowouts for this property.

SUMMARY

The disclosure presents reversible aminal gels produced from thecondensation of aldehydes and amines, which in some embodiments haveapplication to hydrocarbon-producing reservoirs where smart, stimulusresponsive materials are sought. In example embodiments, compositionsdescribed here exhibit dynamic responsivity to certain divalent andtrivalent metal salts. Examples show the utility of metals in themodification of the kinetics and thermodynamics of hemiaminal and aminalinclusive constitutionally dynamic materials (CDMs). The introduction ofmetal salts to certain systems provides a handle to exploit phase changedynamics and mechanical properties of these dynamic materials.

Constitutionally dynamic hemiaminal gels produced from the condensationof aldehydes and amines to aminals can be well suited to the harshenvironments of hydrocarbon-producing reservoirs. In some embodiments,the gels break down when exposed to low pH conditions, for example, withLewis or Bronsted acids. In some embodiments, at neutral pH and greater,they are strong, highly resilient gels with a greater melting point, insome embodiments greater than about 200° C. When a low value pH fluid orappropriate metal salt composition (having a metal ion with a valence 3,4, or 5 (described throughout alternatively as M(+III), M(+IV), orM(+V)), optionally a transition metal complex, is in contact withcertain embodiments of the gels, a condensation reaction is reversed anda complex, optionally involving the metal ion, and optionally atransition metal ion, forms where the gel is transformed into a liquid.Aminal gels can have applications as work-over and completion pills (forexample kill pills), sand control agents, conformance gels, cementadditives, and shale inhibitors in water-based drilling muds.

Precise control of fluid rheologies and liquid-solid phase transitionsunderlie the chemical foundation for safe and effective oil wellconstruction, production, and remediation. Constitutionally dynamicmaterials (CDMs) in wellbore operations offer the possibility to broadenthe performance window of many upstream chemical processes in the oiland gas industry. Materials that are constitutionally dynamic utilizereversible covalent bonding in addition to or alternative tonon-covalent bonding such that the dynamic material undergoes continuouschanges to its constitution through the dissociation and re-associationof its constituent building blocks. These attributes, in part, open up awide variety of possibilities for accessing triggered additive release,reversible gels, and self-healing composites.

CDMs are a class of dynamic materials that comprise both molecular andsupramolecular polymers. The monomeric units of these kinds of polymersare brought together with reversible molecular (covalent) bonding orsupramolecular bonding (which is inherently reversible). CDMs generatedby the reversible covalent association of organic and organometallicbuilding blocks are marked by stronger bonding than their supramolecularcounterparts and have the additional flexibility of access to a greatervariety of dynamic chemical reactions.

Presently, chemicals used to perform wellbore operations are based uponconstitutionally static structures (non-reversible), which in the caseof a sealant limit the ability of the material to self-heal. Theinclusion of self-healing sealants or dynamic, stimulus responsiveadditives in cements could provide unique advantages in oil well cementsor resin sealants where static materials cannot deliver.

Furthermore, processes used to clean a wellbore during completionprocesses can require reversibly gelled liquids. This reversible phasetransformation is of particular utility in the process of perforating;for example, if the losses of completion brine are greater, gels aredeployed to serve as a secondary fluid system, placed across theperforated interval to seal perforations against fluid loss to theformation. Dynamic chemical systems offer new methods for “breakinggels” and the possibility for widening the performance window ofreversible gels deployed in completions.

The compositions described here have been developed in the interest ofinstructing the dynamics of aminals with metals, a hemiaminal polymergel, produced through the condensation of a multifunctional amine andformaldehyde. The hemiaminal gel described converts into a liquidthrough the addition of a trivalent metal. Surprisingly, the resultingorganometallic liquid can then be thermally transformed with acontrolled and modifiable gelation time into a different kind of gelwith enhanced physical properties. This gel can then be transformed backinto a liquid through the addition of a reactive compound such as athiol or phosphine.

The fluid and gel compositions described here may be used in the oilfield through methodologies described for completions fluids, workoverfluids, packer fluids, primary oil well cementing, and remedial oil wellcementing. The gels described are chemically reversible and demonstratehigh thermal stability (up to about 200° C.), which exceeds manycurrently used gels in wellbore construction fluids. The reversibilityof the gels limits formation damage.

The gels can be formed with a controllable, tunable gel-time. They canbe converted into gels in-situ, downhole or made into gels prior topumping into the well. When made into gels prior to placement, they canbe rendered into gel particles which can serve as reversible fluid lossadditive gels. They can be used directly in a drilling fluid, acompletion fluid, workover fluid, or gravel packer or administrated as afluid loss pill.

The gels described are produced, in some embodiments, from triazinecompounds which serve as a second layer of protection to H₂S in the caseof a well blowout. Triazines are organic ringed molecules which havealso been used for H₂S mitigation. H₂S incorporates into the ringstructure of triazines. The base of the gels, in some embodiments, isNMP which provides a primary layer of protection to H₂S by absorbing thegas.

The gels can also be used in a method of remedial cementing where highthermal stability is sought to repair damaged cement seals andmicro-annuli. The controllable gel-time of the materials can enable theuse of these materials in conformance gels and as primary sealants inwellbore construction.

Therefore as disclosed, embodiments include a well treatment compositionfor use in a hydrocarbon-bearing reservoir comprising a reversibleaminal gel composition. The reversible aminal gel composition includes aliquid precursor composition, the liquid precursor composition operableto remain in a liquid state at about room temperature, where the liquidprecursor composition comprises: an organic amine composition; analdehyde composition; a polar aprotic organic solvent; and a metal saltcomposition with valence 3, 4, or 5. The liquid precursor compositiontransitions from the liquid state to a gel state responsive to anincrease in temperature from the hydrocarbon-bearing reservoir. The gelstate is stable in the hydrocarbon-bearing reservoir at a temperaturesimilar to a temperature of the hydrocarbon-bearing reservoir, and thegel state is operable to return to the liquid state responsive to achange in the hydrocarbon-bearing reservoir selected from the groupconsisting of: a decrease in pH in the hydrocarbon-bearing reservoir, anaddition of excess metal salt composition in the hydrocarbon-bearingreservoir, and combinations thereof.

In some embodiments, the organic amine composition comprises a primaryamine of polypropylene glycol with an approximate molecular weight offrom about 280 to about 100,000 Daltons (Da). In other embodiments, theorganic amine composition comprises a primary amine of polyethyleneglycol with an approximate molecular weight of about 200 to about100,000 Da. Still in other embodiments, the organic amine compositioncomprises a primary amine of an aromatic system.

In certain embodiments, the organic amine composition comprises anaminated polyethylene glycol with an approximate molecular weight ofabout 200 to about 100,000 Da, a primary amine of polypropylene glycolwith an approximate molecular weight of about 280 to about 100,000 Da,and oxydianiline. Still other embodiments further comprise a hemiaminalor aminal gel formed at least in part by exchange of aninitially-condensed amine, the initially-condensed amine selected fromthe group consisting of: alkylethylenediamine, benzylethylenediamine,phenylethylene diamine, and mixtures thereof. The initially-condensedamine can be exchanged with a composition selected from the groupconsisting of polyethylene glycol, polypropylene glycol, oxydianiline,and mixtures thereof.

In certain embodiments, the aldehyde composition comprises a compoundselected from the group consisting of: formaldehyde, paraformaldehyde,phenol formaldehyde, resorcinol-formaldehyde, and phenyl acetate-HMTA(hexamethylenetetramine). In some embodiments, the polar aprotic organicsolvent comprises a compound selected from the group consisting of:N-alkylpyrrolidone, N,N′-dialkylformamide, and dialkylsulfoxide. Stillin other embodiments, the metal salt composition with valence 3, 4, or 5comprises a metal selected from the group consisting of: iron(III) andaluminum(III). In other embodiments, the addition of a metal salt isoperable to modify the mechanical properties of the gel to render aself-healing material. Self-healing can refer to the spontaneousformation of new bonds when old bonds are broken within a material.Still yet other embodiments further comprise a gel time acceleratingadditive comprising sodium sulfite. Still in other embodiments, the gelstate comprises triazine-based molecules.

In certain embodiments, the polar aprotic organic solvent comprisesN-vinyl pyrrolidone and is operable to be polymerized through a radicalinitialized reaction. In other embodiments of the composition, N-vinylpyrrolidone is copolymerized with a second monomer thereby modifyinghydrophilicity of a gel matrix and altering a release profile of cargoupon time delayed or triggered release. In some other embodiments, thesecond monomer comprises N-butyl acrylate. Still in yet otherembodiments, N-vinyl pyrrolidone is polymerized as either a homopolymeror a copolymer through radical initiation with potassium persulfate.While in other embodiments, N-vinyl pyrrolidone is polymerized as eithera homopolymer or a copolymer through radical initiation with ultraviolet(UV) light.

In some embodiments of the composition, N-vinyl pyrrolidone ispolymerized as either a homopolymer or a copolymer in a photosensitizedgel through radical initiation with light of a wavelength greater thanabout 350 nanometers (nm). In some embodiments, the gel state is stablebetween about 110° C. and about 250° C. In other embodiments, a molarratio of the organic amine composition to the aldehyde composition tothe polar aprotic organic solvent is between about 1:2:1 and about1:200:500. Still other embodiments further comprise delayed releasecapsules comprising a compound selected from the group consisting of:acidic solution and a metal salt composition.

Additionally disclosed is a method for introducing a reversible aminalgel composition into a wellbore in a hydrocarbon-bearing reservoir. Themethod includes the steps of: injecting a reversible aminal gelcomposition into the hydrocarbon-bearing reservoir, the reversibleaminal gel composition comprising: a liquid precursor composition, theliquid precursor composition operable to remain in a liquid state atabout room temperature, where the liquid precursor compositioncomprises: an organic amine composition; an aldehyde composition; apolar aprotic organic solvent; and a metal salt composition with valence3, 4, or 5; and allowing the liquid precursor composition to transitionfrom the liquid state to a gel state responsive to an increase intemperature from the hydrocarbon-bearing reservoir. The method furtherincludes the step of returning the gel state to the liquid state bychanging a property in the hydrocarbon-bearing reservoir selected fromthe group consisting of: pH in the hydrocarbon-bearing reservoir, anamount of metal salt composition in the hydrocarbon-bearing reservoir,and combinations thereof.

In some embodiments, the method further comprises the step of adding agel time accelerating additive comprising sodium sulfite. In someembodiments, the polar aprotic organic solvent comprises N-vinylpyrrolidone and is operable to be polymerized through a radicalinitialized reaction. In some embodiments, N-vinyl pyrrolidone iscopolymerized with a second polymer thereby modifying hydrophilicity ofa gel matrix and altering a release profile of cargo upon time delayedor triggered release. In certain embodiments, the second polymercomprises N-butyl acrylate. Still in other embodiments, the methodfurther comprises the step of polymerizing N-vinyl pyrrolidone as eithera homopolymer or a copolymer through radical initiation with potassiumpersulfate.

In certain embodiments, the method further comprises the step ofpolymerizing N-vinyl pyrrolidone as either a homopolymer or a copolymerthrough radical initiation with UV light. In some embodiments, themethod further comprises the step of polymerizing N-vinyl pyrrolidone aseither a homopolymer or a copolymer in a photosensitized gel throughradical initiation with light of a wavelength greater than 350 nm. Inother embodiments, the method further comprises the step of maintaininga stable gel state between about 100° C. and about 250° C. Still inother embodiments, the method further comprises the step of adjusting arate of cargo release from the reversible aminal gel composition, wherethe reversible aminal gel composition comprises a cargo to carry out awellbore function selected from the group consisting of: modifyingviscosity of a wellbore fluid; initiating a cement set; and modifyingyield point of a wellbore fluid.

In some embodiments, a molar ratio of the organic amine composition tothe aldehyde composition to the polar aprotic organic solvent is betweenabout 1:2:1 and about 1:200:500. Still in other embodiments, the methodfurther comprises the step of adding delayed release capsules comprisinga compound selected from the group consisting of: acidic solution and ametal salt composition with valence 3, 4, or 5. Some embodiments includethe step of adjusting a ratio of components in the liquid precursorcomposition to tune a temperature at which the reversible aminal gelcomposition reverses to the liquid state. Other embodiments include thestep of adjusting a ratio of components in the liquid precursorcomposition to tune a pH at which the reversible aminal gel compositionreverses to the liquid state. Still other embodiments include the stepof adjusting a ratio of components in the liquid precursor compositionto modify the concentration of excess metal salt required to transformthe reversible aminal gel composition into the liquid state.

In some embodiments of the method, the method includes the step ofadjusting a ratio of components in the liquid precursor composition toalter the amount of time required for a liquid hemiaminal gel form totransform into a greater melting point gel form. Some embodimentsincludes the step of adjusting a ratio of components in the liquidprecursor composition to tune physical properties of the gel state byexchange and reduction in an amount of polar aprotic organic solventrequired for producing a homogenous gel. Still in other embodiments, theorganic amine composition comprises a tris primary amine ofpolypropylene glycol with an approximate molecular weight of betweenabout 280 and about 100,000 Da. In some embodiments, the organic aminecomposition comprises a bis primary amine of polyethylene glycol with anapproximate molecular weight of between about 200 and about 100,000 Da.

In some embodiments of the method, the aldehyde composition comprises acompound selected from the group consisting of: formaldehyde,paraformaldehyde, phenol formaldehyde, resorcinol-formaldehyde, andphenyl acetate-HMTA. Still in other embodiments, the polar aproticorganic solvent comprises a compound selected from the group consistingof: N-alkylpyrrolidone, N,N′-dialkylformamide, and dialkylsulfoxide. Insome embodiments, the metal salt composition comprises a metal selectedfrom the group consisting of: iron(III) and aluminum(III). Otherembodiments of the method include the step of adding a gel timeaccelerating additive comprising sodium sulfite to thehydrocarbon-bearing reservoir. In some embodiments, the gel statecomprises triazine-based molecules.

Still other embodiments further comprise the step of maintaining astable gel state between about 110° C. and about 250° C. In certainembodiments, a molar ratio of the organic amine composition to thealdehyde composition to the polar aprotic organic solvent is betweenabout 1:2:1 and about 1:200:500. Still in other embodiments, the step ofadding delayed release capsules to the hydrocarbon-bearing reservoircomprising a compound selected from the group consisting of: acidicsolution and a metal salt composition is included in the method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescriptions, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of thedisclosure and are therefore not to be considered limiting of thedisclosure's scope as it can admit to other equally effectiveembodiments.

FIG. 1A shows a partial reaction scheme of the mechanism for thecondensation of formaldehyde with organic amines to produce a series ofaminals and hemiaminals.

FIG. 1B shows a partial reaction scheme of the mechanism for thecondensation of formaldehyde with organic amines to produce a series ofaminals and hemiaminals, along with a greater melting pointtriazine-based gel (H).

FIG. 2 shows a reaction scheme mechanism for the transformation of thetransitory products from FIGS. 1A and 1B.

FIG. 3 shows a graphic representation for certain possible phase changesduring the formation of gels of the present disclosure.

FIG. 4 shows a reaction scheme for the formation of a stimulusresponsive low melting point aminal gel based on aminal chemistry.

FIG. 5 shows a reaction scheme intermediate step for the formation of agreater melting point gel in the presence of iron(III).

FIG. 6 shows a reaction scheme for one proposed formation of a greatertemperature melting point triazine-based gel in the presence ofiron(III) after exposure to 150° C. heating.

FIG. 7 shows a reaction scheme for one proposed method to reverse theformation of a greater temperature melting point triazine-based gel inthe presence of excess iron(III).

FIG. 8A shows a pictorial representation of Experiment II-F, in whichdisintegration of aluminum triazine greater temperature melting pointgel was tested.

FIG. 8B shows a pictorial representation of Experiment II-F, in whichdisintegration of aluminum triazine greater temperature melting pointgel was tested.

FIG. 8C shows a pictorial representation of Experiment II-F, in whichdisintegration of aluminum triazine greater temperature melting pointgel was tested.

FIG. 9 is a graph showing the storage modulus versus temperature forgels formed with differing molar ratios of JEFFAMINE® to N-methylpyrrolidone (“NMP”), according to experiments using embodiments of thepresent disclosure.

FIG. 10 is a reaction schematic diagram showing equilibrium dynamics ofcertain metalloaminal gels.

FIG. 11 is a reaction schematic diagram showing molecular structureswhich predominate in certain gel formation processes of the presentdisclosure.

FIG. 12 is a graph showing the time dependence of rheology for the gelformulation described in Table 2 at various temperatures.

FIG. 13 is a graph showing the viscosity versus time for a sample gelwith 24.4 molecular equivalents of sodium sulfite (to JEFFAMINE®) andfor a sample gel without sodium sulfite.

FIG. 14 is a graph showing the effect of increasing aluminum chloridecontent on gel time at 68° C.

FIG. 15 is a graph showing the effect of increasing ferric ammoniumsulfate concentration on gel time at 69° C.

FIG. 16 is a graph plotting the relative gel times for hemiaminal gelscomplexed with aluminum(III) and iron(III).

FIG. 17 is a graph showing storage modulus and loss modulus results at72° C. and 115° C. for the results of Experiment II-E.

FIG. 18 is a graph showing gelation time of a 65:5 gel with 1.2equivalents (eq.) of AlCl₃ by showing increase in modulus over time.

FIG. 19 is a graph showing the cross-over point A of the storage modulusand the loss modulus at about 120° C. for the sample of FIG. 18.

FIG. 20 is a graph showing time resolved ultraviolet-visible (“UV/VIS”)spectra for the release of LOMAR® D and the disintegration of ahemiaminal gel in water. After 2 hours, the gel had completelydisintegrated and was no longer visible in the liquid.

FIG. 21 is a graph showing time resolved UV/VIS spectra for the releaseof LOMAR® D and the disintegration of a hemiaminal gel in NMP.

FIG. 22 is a graph showing time resolved UV/VIS spectra for the releaseof LOMAR® D and the disintegration of a hemiaminal gel in NMP withAlCl₃.

FIG. 23 is a graph showing time resolved UV/VIS spectra for the releaseprofile for an NVP (“N-vinyl pyrrolidone”)/N-butyl acrylatepolymer-hemiaminal system in water.

FIG. 24 is a graph showing the melting point trend as a function ofamine:aldehyde ratio for hemiaminal gels of the present disclosure.

FIG. 25A is a graph showing an amplitude sweep of sample A-1 fromGeneral Chemical Method II.

FIG. 25B is a graph showing an amplitude sweep of sample A-2 fromGeneral Chemical Method II.

FIG. 25C is a graph showing an amplitude sweep of sample A-3 fromGeneral Chemical Method II.

FIG. 25D is a graph showing an amplitude sweep of sample A-4 fromGeneral Chemical Method II.

FIG. 25E is a graph showing stabilization of gel rheological propertiesafter temperature stabilization at 25° C. for sample A-1.

FIG. 25F is a graph showing stabilization of gel rheological propertiesafter temperature stabilization at 25° C. for sample A-2.

FIG. 25G is a graph showing stabilization of gel rheological propertiesafter temperature stabilization at 25° C. for sample A-3.

FIG. 25H is a graph showing stabilization of gel rheological propertiesafter temperature stabilization at 25° C. for sample A-4.

FIG. 26A is a graph showing phase shift angle versus shear strain forsample A-5 alone, sample A-5 with 0.2 grams of Mohr's salt, and sampleA-5 with 0.8 grams of Mohr's salt.

FIG. 26B is a graph showing phase shift angle versus shear strain forsample A-3 alone and sample A-3 with iron(II).

FIG. 27A is a pictorial representation of the addition of a trivalentmetal salt, ferric ammonium sulfate, to samples A-1 through A-5.

FIG. 27B is a pictorial representation of the addition of a trivalentmetal salt, ferric ammonium sulfate, to samples A-1 through A-5.

FIG. 28A is a pictorial representation of gel sample A-1 becoming aliquid after reaction with aluminum chloride hexahydrate.

FIG. 28B is a pictorial representation of gel sample A-1 returning to agel state after being heated to 70° C.

FIG. 28C is a pictorial representation of gel sample A-1 returning to aliquid state after the addition of phosphine in NMP to the gel in FIG.28B.

FIG. 29A shows the results of a small amplitude oscillatory rheometryexperiment in which different amounts of aluminum chloride were added tothe same gel composition.

FIG. 29B shows the results of a small amplitude oscillatory rheometryexperiment in which different amounts of aluminum chloride were added tothe same gel composition, and the resulting gel time for theorganometallic liquid at 70° C. was recorded. Increasing amounts ofaluminum chloride increase the gel time.

FIG. 30 shows a reaction scheme for a reversible gel, optionally for usein situ as a kill pill in a hydrocarbon-bearing reservoir.

FIG. 31 is a graph showing gelation time for certain reversible gels ofthe present disclosure at 70° C., 100° C., and 150° F., while maintainedat 3.4 Megapascal (MPa) pressure.

FIG. 32 is a graph showing gelation time for certain reversible gels ofthe present disclosure at 20 MPa, 35 MPa, and 60 MPa, while maintainedat 70° C.

FIG. 33 shows a core-flood set-up for demonstrating the ability oftris(2-carboxyethyl)phosphine (TCEP) or NMP/TCEP to serve as a gelbreaker for a 65-5 metal-salt-stabilized thermodynamic gel.

FIG. 34 is a graph showing the results of testing of the gel breakingability of TCEP in a Grace 9100 Core Flow apparatus, shown in FIG. 33.

DETAILED DESCRIPTION

So that the manner in which the features and advantages of theembodiments of compositions, systems, and methods of reversible aminalgels, as well as others, which will become apparent, may be understoodin more detail, a more particular description of the embodiments of thepresent disclosure briefly summarized previously may be had by referenceto the embodiments thereof, which are illustrated in the appendeddrawings, which form a part of this specification. It is to be noted,however, that the drawings illustrate only various embodiments of thedisclosure and are therefore not to be considered limiting of thepresent disclosure's scope, as it may include other effectiveembodiments as well.

Some embodiments include varying the relative quantity of a polaraprotic organic solvent component (such as N-methyl pyrrolidone (“NMP”),N-vinyl pyrrolidone (“NVP”), dimethylformamide (“DMF”),dimethylsulfoxide (“DMSO”), or similar polar aprotic organic solvents ormixtures of solvents) to adjust the melting point of a gel. Otherembodiments include modifying the structure of an amine precursor to theaminal or hemiaminal gel to tune the melting point of the gel. Themelting point of a greater temperature melting point gel of the presentdisclosure can be between about 50° C. and about 100° C., between about75° C. and about 150° C., between about 100° C. and about 175° C.,between about 125° C. and about 200° C., and between about 150° C. andabout 250° C.

In certain embodiments, heating of organometallic fluids results in theformation of a second type of gel with a greater melting point anddifferent mechanical properties. In the disclosure, an organometallicfluid is defined as any fluid in which the organic components bind witha metallic component. Gel formation times can be regulated by changes intemperature and through the addition of reducing agents such as sodiumsulfite. Organometallic gels can be transformed back into a fluid byfurther addition of an M(+III), in addition to or alternative to adecrease in pH.

Chemistries have been developed and are disclosed that enable dynamic,stimulus responsive gels. In some embodiments, a hemiaminal gel,produced through the condensation of a polyamine and an aldehyde, suchas formaldehyde or paraformaldehyde (containing some percentage offormaldehyde), can be converted into a liquid through the addition of atrivalent metal. The resulting organometallic liquid can then bethermally transformed with a controlled and modifiable gel time into adifferent kind of gel with enhanced physical properties. This gel canthen be transformed back into a liquid through the addition of excesssolvent used to produce the gel along with heat. Certain chemistriesdescribed in this disclosure may have application to completion fluidswhere breakable gels are required, to self-healing composites for zonalisolation, and to oil well cements where delayed and controlled releaseof additives is sought.

Hemiaminal gels can be transformed into liquids through the addition oftrivalent metals, such as aluminum or iron. The resulting organometallicliquid can be referred to as a metalloaminal gel and can be transformedinto a different gel with unique physical properties through heating.The gel time for this transformation can be controlled and modified asneeded by adjusting the amount of trivalent metal in the liquid orthrough the addition of an accelerator such as sodium sulfite. Aluminumchloride, in some embodiments, acts as both an accelerator to gelformation, catalyzing formation of a triazine complex, and as a retarderby stabilizing reactants prior to the triazine product.

Without being bound by any theory or principle, the action of aluminumchloride is believed to occur because a trivalent metal (or “M(+III)”)stabilizes the transition state and lessens the activation energy forthe ring closure of product G to product H in FIG. 1B (discussed furtherwith regard to FIG. 1B as follows). An M(+III) also stabilizes a liquidprecursor by binding to any one of the structures from A to F in FIGS.1A and 1B, and thereby lessens the energy of the precursor materialsrelative to the ring-closed triazine. This stabilization retards theformation of product H because the relative activation energy requiredis increased by the lessening of the free energies of the structuresresponsible for the liquid state.

In some embodiments, ferric ammonium sulfate does not accelerate theformation of a triazine (product H in FIG. 1B, also referred to as atrisubstituted hexahydrotriazine) as effectively as aluminum chloride.The addition of increasing amounts of ferric ammonium sulfate tosolution leads to a decrease in the rate of formation of triazine. Thismay occur through the same mechanism as the retardation of the productformation in the case of aluminum.

In some embodiments, a hemiaminal gel can be made with a melting pointexceeding about 78° C. The hemiaminal gel is easily broken down to aliquid with the addition of aluminum chloride either as a solid or as asolution in water or NMP. The liquid then gives reliable gel times tothe formation of a triazine-based gel. At about 110° C., thistriazine-based gel has a greater melting point than the hemiaminal gel.In some embodiments, a triazine-containing gel has a melting pointgreater than about 110° C., and in other embodiments, atriazine-containing gel has a melting point greater than about 200° C.Stirring a reaction product with heat and excess solvent (NMP)eventually transforms a triazine-containing gel back to a liquid.Addition of an acid, such as hydrochloric acid, can also transform agreater melting point triazine-based gel back to a liquid by a reductionin pH.

In some embodiments, metals introduced to the hemiaminal/aminal systemalter the dynamics of gel formation. The use of a metal saltcomposition, in addition to or alternative to transition metals, incertain systems enables the rendering of greater melting point gels forthe use of the disclosed chemistry in a wide variety of well conditions.Some embodiments include the use of an available JEFFAMINE® product asaminated polyethers in the hemiaminal/aminal gel systems described.Other embodiments include the use of aromatic amines such asoxydianiline (“ODA”). In some embodiments, aldehyde alternatives can beused in addition to or alternative to formaldehyde and paraformaldehyde,such as phenol formaldehyde, resorcinol-formaldehyde, and phenylacetate-HMTA. In some embodiments, the reversible gels of the presentdisclosure are used as diversion materials in fracturing applications inhydrocarbon-bearing reservoirs.

In embodiments of the disclosure, useful aminated polyethers (includingaminated polyethylene glycols and aminated polypropylene glycols) can bebranched or straight chained. Some embodiments include polyalkyleneethers such as polypropylenes, polypropylene oxides, polybutylenes,polybutylene oxides, polyethyleneimines, and polyethylene oxides.Alternatives to aminated polyalkylene ethers include aromatic polyaminessuch as oxydianiline, diaminobenzene, diaminonapthalene, and aminatedpyrene. Other alternatives to aminated polyalkylene ethers includeaminated graphene, aminated carbon fibers, and amine functionalizednanoparticles (such as ZrO₂, SiO₂, TiO₂, superparamagnetic iron oxidenanoparticles, single wall carbon nanotubes, multiwall carbon nanotubes,carbon nanohorns, and single wall carbon nanotubes).

Gels of the present disclosure may be reinforced with carbon fibers,glass fibers, carbon nanofibers, carbon nanotubes, silica fume, silicaparticles, or other particulates or nanoparticulates.

In certain embodiments, the addition of a divalent metal, such asiron(II), results in the modification of the mechanical properties ofthe gels. These modifications can include imparting self-healingproperties into the gel such that when the gel is broken or cut, the gelcan re-mend itself when the two broken gel components are brought intophysical contact with one another.

In other embodiments, the gels serve as stimulus responsive containersthat when laden with cargo and in the presence of an appropriatestimulus can release their contents to the surrounding environment overa pre-determined or specified time. This environment could be a solid,liquid, or gas environment. In this way, the timed release of chemicaladditives may be achieved through the controlled break down ofcargo-laden gels of hemiaminal or aminal composition at controllablemelting points.

In certain embodiments, a solvent or solvent mixture can be modified toalter the release profile of the cargo. For instance, N-vinylpyrrolidone (“NVP”) can be used as a solvent and co-polymerized withN-butylacrylate in the production of a gel. In this way, while theorganoamines are condensing with formaldehyde, NVP polymerizes withN-butylacrylate. This cross-linked web of what would otherwise be thesolvent in the gel serves to reduce the permeability and responsivenessof the gel to cargo release. In some embodiments, the radicalpolymerization of the pyrrolidone co-polymer may be actuated withradical initiators such as potassium persulfate. In other embodiments,the radical polymerization reaction may be initiated with UV light. Inother embodiments, the radical polymerization reaction may be initiatedwith visible or near-infrared (“NIR”) light through photosensitizationof the gel to the appropriate wavelength of the light.

As disclosed, embodiments include a gel produced through thecondensation of an aldehyde and an organic amine where the addition of atrivalent metal results in the transition of the material to a liquid.Other embodiments include the conversion of this liquid into a gelthrough heating. Other embodiments include the reconversion of thissecond/thermodynamic gel to a liquid through combination with a polaraprotic solvent.

In other embodiments, the hemiaminal or aminal gel is formed at least inpart by exchange of the amine from a previously formed hemiaminal oraminal gel composition. The initially-condensed amine can be selectedfrom the group consisting of: alkylethylenediamine,benzylethylenediamine, phenylethylene diamine, and mixtures thereof.This initial amine is exchanged with an aminated polyethylene glycol,polypropylene glycol, or other polyalkylene glycol.

Certain dynamic gels disclosed here are produced through a condensationof an aldehyde, such as formaldehyde or paraformaldehyde, with anorganic amine. Organic amines include aliphatic and aromatic aminatedpolymers. Certain mechanisms for this reaction are illustrated in FIGS.1A, 1B, and 2. In the exemplified condensation reaction, product H isthe thermodynamic product. The other reaction products A-G are kineticproducts and are present in the pre-equilibrium reaction product invarying degrees. The concentration distribution of kinetic products canbe shifted by a change in pH or through the addition of a molecule thatcan act as a receptor for any of the reaction products, A through Hdepicted in FIGS. 1A and 1B.

When a molecule binds to any one of the reaction products, it affectsthe free energy of the complex and changes the equilibria and activationenergies of the formaldehyde/amine condensations. The presence of adifferent component can then be amplified relative to the others. Forexample, product A could be amplified over product G. One outcome ofreaction schemes shown in FIGS. 1A, 1B, and 2 is that the physicalproperties (such as mechanical strength and melting point) of a gel orresin produced from these dynamic building blocks can be altered when inthe presence of a chemical stimulus.

Experimental Methods and Results

In FIGS. 1A and 1B, a reaction scheme is provided of the mechanism forthe condensation of formaldehyde with organic amines to produce a seriesof aminals and hemiaminals. FIG. 2 shows a reaction scheme mechanism ofhow the transitory products from FIGS. 1A and 1B transform into and fromone another. Certain example solvents that have been tested for thechemistries described throughout the disclosure are N-methylpyrrolidone(“NMP”), N,N′-dimethylformamide (“DMF”), and dimethylsulfoxide (“DMSO”).In other embodiments, other polar aprotic organic solvents orcombinations of solvents could be selected by one of ordinary skill inthe art. N-methyl pyrrolidone, paraformaldehyde, sodium sulfite,aluminum chloride hexahydrate, and ferric ammonium sulfate dodecahydratewere purchased from Fisher Scientific Co. LLC. JEFFAMINE® T-5000 wasobtained from Huntsman International LLC.

Referring now to FIG. 3, a graphic representation is shown for certainpossible phase changes during the formation of gels of the presentdisclosure. As related to FIGS. 1A and 1B, in FIG. 3 Gel I correspondsto a gel, such as reaction product G in FIG. 1B, produced by thereaction of an organic amine and an aldehyde, such as paraformaldehydeor formaldehyde. As is shown generally in FIG. 3, Gel I, or the reactionproduct G in FIG. 1B, can be further modified by a metal saltcomposition M(+III) and heat to produce Gel II, or reaction product H inFIG. 1B, which itself can be returned to a liquid form, shown as LiquidII (see also FIG. 10).

In some embodiments, the gels represented by Gel II in FIG. 3 are solidsat mildly acidic pH, neutral pH, and greater pH (in basic solution), andthe gels can become a liquid at low pH (in acidic solution), or whenexcess iron, metal salt composition, or transition metal complexes, areadded to them. For example, solid gels could be removed from a well byadding acid or excess transition metal complexes or metal saltcompositions with valence 3, 4, or 5. The gels represented by Gel II inFIG. 3 and reaction product H in FIG. 1B can be greater melting pointtriazine-based gels, optionally complexed with a trivalent metal from ametal salt composition with valence 3, 4, or 5.

FIG. 4 shows a reaction scheme for the formation of a stimulusresponsive aminal gel based on aminal chemistry. In FIG. 4, I representsJEFFAMINE®, II represents formaldehyde, III represents NMP, IVrepresents an initial aminal gel (without any substantial triazine ringformation), and H₂O represents excess water. NMP is a solvent. In thereaction scheme of FIG. 4, a low melting point gel IV is formed, whichbecomes a liquid when heated to about 50° C.

In applications, such as conformance gels, where long-term solutions aresought to shut off water and gas zones of hydrocarbon-producingreservoirs, gels may be obtained by mixing of JEFFAMINE® (I) withformaldehyde (II) and N-methylpyrrolidone (III) (see FIG. 4) to producea gel with strong resilient properties. In order to meet therequirements of greater-temperature, hydrocarbon-producing well andreservoir conditions (greater than about 100° C.), the melting point ofaminal gels can be increased by heating the material in the presence ofmetal salt compositions with metal ions having a valence 3, 4, or 5(also referred to as M(+III), M(+IV), or M(+V), respectively),optionally transition metal compounds, such as an iron(III) compound.

In some embodiments, 1.1 molar equivalents of iron(III) to JEFFAMINE® issufficient to convert aminal gels to free flowing liquids at roomtemperature. In some embodiments, an optimal molar ratio for theformation of the greater melting point temperature triazine-based gelsis 1:5.4:250 of JEFFAMINE® T5000:Paraformaldehyde:NMP. JEFFAMINE® T-5000polyetheramine is a trifunctional primary amine of approximately 5,000Da molecular weight. It is a clear, almost colorless, viscous, liquidproduct, and is produced by Huntsman International LLC. Unless specifiedotherwise in context, molecular weight values in this disclosure referto weight average molecular weights. In FIGS. 4 and 5 in JEFFAMINE® (I),x+y+z is about equal to 85, in some embodiments.

Referring now to FIG. 5, a reaction scheme intermediate step is shownfor the formation of a greater melting point gel in the presence ofiron(III). In FIG. 5, I represents JEFFAMINE®, II representsformaldehyde, III represents NMP, and V represents an organometallicintermediary compound. When iron(III) is added to the hemiaminal gelscheme in FIG. 4 (shown by FIG. 5), the gel transitions to a solution atroom temperature shown by organometallic intermediary compound V in FIG.5. If a small amount of iron(III) is used to break the initial lowmelting point gel (IV), then when the solution is later heated to 150°C., a greater melting point gel reforms (VI) (as shown in FIG. 6).

Referring now to FIG. 6, a reaction scheme is shown for one proposedformation of a greater temperature melting point gel in the presence ofiron(III) after exposure to 150° C. heating. In FIG. 6, V represents theorganometallic intermediary compound from FIG. 5, II representsformaldehyde, III represents NMP, and VI represents a greater meltingpoint triazine-based gel. This gel, represented by VI, has asubstantially greater melting point than the initial hemiaminal gel,represented by IV in FIG. 4. Without being bound by any theory orprinciple, it is believed that some other species are formed on heating(for some of the material in the gel, a triazine-based structure). Agreater melting point is observed in the gel VI, greater than about 200°C.

When 1.4 equivalents (to JEFFAMINE®) of FeCl₃ are added to the neat gelIV represented in FIG. 4, and the solution is heated to 150° C. for 20minutes as shown in FIG. 6, a color change is observed from bright redto a deep, dark red. One result of the heating step is that the gelreforms as a greater melting point gel. While the melting point of thehemiaminal gel (initial gel IV) was about 50° C., the melting point ofthe greater melting point gel VI exceeds the boiling point of the NMPsolvent, where the boiling point of NMP solvent is greater than about200° C. In some embodiments of the greater melting point gel VI, themelting point exceeds about 200° C., and in other embodiments, themelting point exceeds about 100° C. It is believed one contributingfactor to the physical property change of the gel could correspond tothe formation of a triazine core in some of the species comprising thegel, optionally complexed with the metal of the metal salt (see alsoFIG. 10).

Gels derived from the chemistries of the present disclosure areconstitutionally dynamic and based on reversible covalent chemistry.While present in environments at mildly acidic pH, neutral pH, andgreater pH (alkaline or basic environments), they are strong gels. If aBronsted or Lewis acid such as concentrated hydrochloric acid or irontrichloride in excess is added to the greater melting pointtriazine-based gels, they transform themselves into thin fluids. Thisproperty can be useful when applying this technology as workover or killpills. When in the process of perforating a wellbore in ahydrocarbon-bearing reservoir, if the losses of the completion brine aregreater, these gels could serve as a secondary fluid system (fortemporary fluid loss control) placed across the perforated interval toseal perforations against fluid loss to the formation. The gels can thenbe removed through treatment with an acid once the completion process isfinished. Experiments have also shown that when excess iron(III) isadded to greater melting point gel networks, the network breaks down.The proposed reaction scheme is shown in FIG. 7.

Referring now to FIG. 7, a reaction scheme is shown for one proposedmethod to reverse the formation of a greater temperature melting pointgel in the presence of excess iron(III). When excess iron(III) is addedto the greater melting point gel VI in the presence of NMP and water,the structure breaks down to a solution. Similarly, concentratedhydrochloric acid also breaks the greater melting point gel VI and aliquid fluid is formed. In embodiments of the present disclosuretherefore, reversible greater melting point gels are obtainable to meetthe temperature requirements for gels in downhole environments ofhydrocarbon-bearing formations.

When placed in 28% HCl for 1 hour at 90° C., the greater melting pointgel disappeared, as the products likely return to their startingmaterials in solution. Similarly, when 50% by mass of FeCl₃ was added tothe dark red gel and heated to 90° C., the gel became a thin liquid.This indicates that the addition of excess iron(III) can shift theequilibrium to favor structure V in FIGS. 5-7.

Gel Concentration Experiment I

The experiment described in this section is referred to as GelConcentration Experiment I throughout the disclosure. To investigate theinfluence of the concentration of paraformaldehyde and JEFFAMINE®condensation product in NMP on the melting point and rheology of gels,oscillatory shear experiments were performed in an Anton Paar rheometer.The gels that were studied all had the same molar ratio of JEFFAMINE® toparaformaldehyde (1:5.4) but all differed in the molar ratio of NMP toJEFFAMINE®. The molar ratio of JEFFAMINE® to NMP varied from 1:63 to1:315. For all of the gels, NMP and paraformaldehyde were mixed at 60°C. for 40 minutes. JEFFAMINE® T-5000 was then added to the solution andstirred for 30 minutes. The formulations of the gels are shown in Table1.

TABLE 1 Gel formulations for Gel Concentration Experiment I. Molar MassMaterial Ratio (grams (g)) Moles Paraformaldehyde 5.4 0.13 0.00433JEFFAMINE ® T-5000 1 4.0 0.0008 N-Methyl pyrrolidone 63, 189, 315 5, 15,25 0.050, 0.15, 0.25

The gels formulated from Table 1 were heated to 90° C. past theirmelting points. Then, as free flowing liquids, the solutions were pouredinto the rheometer cell of the Anton Paar device, and the temperature ofthe cell was ramped up while monitoring G′ and G″ at 1 Hertz (Hz) and 1%amplitude. This enables the determination of the gel melting points. Theramp rates were 5.9, 1.5, 0.38° Centigrade/minute (° C./min) for sampleswith a 63, 189, and 315 molar ratio of NMP to JEFFAMINE® T-5000,respectively.

Experiment II

Gel Time Experiments for the Transformation of Gels from Hemiaminal toTriazine-Based Gels with Tri-Aminated Polypropylene Glycols

The formulations that follow in Tables 2 through 6 (Experiments II-A, B,C, D, and E) were prepared following a general method which is describedas follows. The gels were synthesized through the addition JEFFAMINE®T-5000 to paraformaldehyde in NMP. JEFFAMINE® T-5000 is a tris primaryamine of polypropylene glycol with an approximate molecular weight of5000 Da. The gel formed from the condensation of paraformaldehyde andJEFFAMINE® T-5000 in NMP is broken down through the addition of aniron(III) or aluminum(III) complex. In these experiments, theorganometallic liquid is then heated. The heating leads to the formationof gels with different physical properties than the initial gels formedprior to the addition of M(+III).

For all of the gels tested in Experiments II-A, B, C, and D, NMP andparaformaldehyde were mixed at 60° C. for 40 minutes. JEFFAMINE® T-5000was then added to the solution and stirred for 30 minutes. The liquidwas then removed from the heating bath and allowed to cool to roomtemperature. After the hemiaminal gel had formed, the metal salt (alsoreferred to as “M(+III)”) was added. The gel was then sliced up with aspatula to increase the surface area available for metal complexation.The gel was digested into a liquid over a period of a few days at roomtemperature through the addition of an M(+III) salt to the gel.

Gel times were determined for the formulations described in Tables 2through 5 with a Brookfield DV2T rheometer with an LV-04 spindle. Therheometer was set to measure viscosity at 12 rotations per minute (rpm)as a function of time. The samples were heated to various temperaturesin oil baths. The temperatures were specified with Fann temperaturecontrollers.

In Experiment II-A, hemiaminal gel samples were treated with iron(III)to become liquids and were then separately heated to 55° C., 75° C., 80°C., and 87° C. The gel times were measured, or in other words the timeperiods to re-form a greater melting point gel were measured. Theformulation for the gel samples studied in Experiment II-A is presentedin Table 2. FIG. 12 is a graph showing the time dependence of rheologyfor the gel formulation described in Table 2 at various temperatures. Asshown by FIG. 12, with greater heating applied, greater melting pointgels formed more quickly.

TABLE 2 Formulation for gel samples in Experiment II-A. Mass MolecularMaterial (grams) Moles Equivalents Ammonium iron(III) sulfate 7.5 0.01561.2 Paraformaldehyde 2.08 0.0693 5.4 JEFFAMINE ® T-5000 64.0 0.0128 1N-Methylpyrrolidone 82.4 (80 0.831 64.9 milliliters (mL))

In Experiment II-B, a gel time accelerating additive, sodium sulfite,was tested. Tests were performed to assess the possibility ofaccelerating the gel formation with an additive. The gel formulation forthe samples in Experiment II-B (using sodium sulfite) is presented inTable 3. The sample was heated to 70° C.

TABLE 3 Formulation for gel samples in Experiment II-B. Mass MolecularMaterial (grams) Moles Equivalents Ammonium iron(III) sulfate 1.720.00357 1.1 Paraformaldehyde 0.52 0.0173 5.4 JEFFAMINE ® T-5000 160.0032 1.0 N-Methylpyrrolidone 82.4 (80 mL) 0.831 260 Sodium Sulfite 9.80.07808 24.4

In Experiment II-C, a demonstration of the effect of aluminum chlorideon gel time was carried out. As shown in the formulation in Table 4,increasing amounts of aluminum chloride were added to the 65:5NMP:paraformaldehyde hemiaminal gel. The resulting liquid was thenheated to 68° C. and the gel time was measured. As used throughout thedisclosure, “65:5” refers to a molar ratio of about 65 NMP to about 5paraformaldehyde.

TABLE 4 Formulations for gel samples in Experiment II-C. Molar MassMaterial Ratio (grams) Moles Paraformaldehyde 5.4 2.08 0.0692JEFFAMINE ® T-5000 1 64.0 0.0128 N-Methylpyrrolidone 64.9 82.4 0.831Aluminum Chloride 1.2, 4.0, 6.8 3.8, 12.7, 21.6 0.0145 Hexahydrate

In Experiment II-D, the effect of ferric ammonium sulfate as a catalystand a retarder for triazine ring closure was tested. The effect ofiron(III) on gel time is observed in this experiment. Similar toexperiment II-C, where the effect of aluminum(III) was observed,increasing amounts of iron(III) are added to the hemiaminal gel as shownin Table 5.

TABLE 5 Formulations for gel samples in Experiment II-D. Material MolarRatio Mass (grams) Moles Paraformaldehyde 5.4 2.08 0.0692 JEFFAMINE ®T-5000 1 64.0 0.0128 N-Methylpyrrolidone 64.9 82.4 0.831 Ferric AmmoniumSulfate 1.1, 1.5, 6.8, 9.25, 11.7, 32.1 0.0192 1.9, 5.2

Experiment II-E compared the effect of aluminum(III) on the relative gelconversion rate of the hemiaminal structure to the triazine structure.Rheologies in Experiment II-E were measured with a Grace InstrumentM5600 HPHT rheometer in oscillatory shear mode (at 1 Hz and 10% strain).The formulations that were prepared were based upon the hemiaminal geldescribed in Table 6. The gel was prepared according to the standardprocedure described for experiment II-A. Two samples were prepared forthis gel. The first gel sample was heated in the M5600 rheometer to 115°C., and the gel time was determined. Then, 1.2 equivalents (toJEFFAMINE®) of aluminum chloride were added to the second sample inorder to produce a room temperature liquid from the sample. It was thenheated to 78° C., and then the gel time was recorded in the M5600rheometer.

TABLE 6 Formulations for gel in Experiment II-E. Material Molar RatioMass (grams) Moles Paraformaldehyde 5.4 2.08 0.0693 JEFFAMINE ® T-5000 164 0.0128 N-Methylpyrrolidone 64.9 82.4 0.831

In Experiment II-F, disintegration of aluminum triazine greatertemperature melting point gel was tested. The aluminum triazine gelformed from experiment II-C (Table 4) with 1.2 equivalents of aluminumchloride was tested for reversibility. In this case, 2.45 grams of thealuminum triazine greater temperature melting point gel was added to 40mL of NMP. The material was heated to 50° C. and stirred. The sample wasstirred at 90° C. over the weekend for about 4 days.

Referring now to FIGS. 8A-C, a pictorial representation is provided ofExperiment II-F, in which disintegration of aluminum triazine greatertemperature melting point gel was tested. The aluminum triazine gel wasplaced into a glass vial equipped with a magnetic stir bar, shown inFIG. 8A. 38 mL of NMP was added to the vial, shown in FIG. 8B. Thesolution was stirred for 4 days at 90° C. After about 4 days' time, thegel was no longer present and the liquid solution turned a darkbrown/red color, shown in FIG. 8C.

The experiments described help explain the nature of the gel formationdynamics. In the experiments described, a water insoluble tris-aminopolypropylene glycol was used as the condensing amine, paraformaldehydewas used as the electrophile, and NMP was used as the solvent. When thehemiaminal gel (see structure G in FIG. 1B) produced from thecondensation is heated to greater than its melting point for an extendedperiod of time, the gel converts into a different kind of gel with agreater melting point and lesser storage modulus than the previous gel.Without being bound to any theory or principle, it is believed that thetriazine core of the modified gel can be responsible, in part, for thegreater melting point gels (see structure H in FIG. 1B).

For the initial low melting point gels prepared in Gel ConcentrationExperiment I, the gel melting points varied from between about 55° C. toabout 79° C. When the ramp rate for the gel is decreased, a differentprofile is observed, and it appears that the gel (JEFFAMINE®T-5000:NMP::1:189) does not lose mechanical properties as anticipatedfor a melting gel. This is one indication of a chemical transformationoccurring. The gel prior to heating is a kinetic gel (likely to bepredominately structure G in FIG. 1B). If it is heated for long enoughand at greater enough temperature, it can transform itself into thethermodynamic greater melting point triazine-based gel (structure H inFIG. 1B).

The rheological profile of the gels tested in Gel ConcentrationExperiment I reveal that decreasing the amount of NMP in a givenhemiaminal gel increases the melting point of the gel (see FIG. 9 andTable 7). The storage modulus of the gel also changes with the amount ofNMP. The loss modulus decreases with a decrease in the relative quantityof NMP while the storage modulus of the hemiaminal gel increases. Thisindicates that the stiffness of the gel is greater at higherconcentrations of organic amine and aldehyde in the polar aproticsolvent.

TABLE 7 Certain physical properties of the gels described in Table 1.NMP:JEFFAMINE ® Storage Modulus/Loss Ratio Melting Point Modulus (Pa) at25° C.  63:1 77-79° C. 1077 189:1 66-67° C. 104.9/0.108 315:1 55-57° C. 92.4/0.274

Referring now to FIG. 9, a graph is provided showing the storage modulusversus temperature for gels with differing molar ratios of JEFFAMINE® toNMP, according to experiments of embodiments in the present disclosure.The molar ratio of JEFFAMINE® to paraformaldehyde in all the gelspresented is 1:5.4. The amount of NMP is variable. The ratio ofJEFFAMINE® to NMP varies from 1:63 to 1:315.

In some embodiments of the present disclosure, it is believed, withoutbeing bound by any theory or principle, that the triazine structure canbe arrived at by other pathways. For example, when an M(+III) compound,such as ferric chloride or aluminum chloride, with an M(+III) ion isadded to a hemiaminal gel, the gel is transformed into a liquid. Afterheating the liquid for a certain period of time, a gel is also formed.The formed gel is believed to be comprised of the triazine (aminal) corestructure with complexation to the metal (see Gel II from Liquid II inFIG. 10).

Referring now to FIG. 10, a reaction schematic diagram is providedshowing equilibrium dynamics of certain metalloaminal gels. Adescription of the effect of M(+III) is presented in FIG. 10. Thebreaking of Gel I occurs, in part, because of the coordination of theCDM and M(+III) to form Liquid II. The coordination occurs because acomponent from the equilibrium shown in FIGS. 1A and 1B that is notcovalently networked as a gel is amplified. Without being bound by anytheory or principle, it is believed the coordination of the CDM andM(+III) is one way in which Gel I is transformed from a solid to LiquidII.

The melting point of a 65:5 gel with the addition of 1.1 equivalents ofAlCl₃ is about 110° C., while the melting point in the absence of thealuminum chloride is about 74° C. Interestingly, when a metal (II)compound, such as ferrous ammonium sulfate, is added to a hemiaminal gel(low melting point gel), the gel is not transformed into a liquid. Thematerial remains as a gel but the mechanical properties are altered. Thegel becomes more self-healing. M(+III) compounds are generally betterLewis acids than metal(II) compounds. Without being bound by any theoryor principle, it is believed that the greater Lewis acidity of M(+III)compounds provides a component for what is required to break the C—Nbonds to make the organometallic complex drawn in FIG. 11, step C.

Referring now to FIG. 11, a reaction schematic diagram is providedshowing certain molecular structures which are believed to predominatein certain gel formation processes of the present disclosure. FIG. 11provides a condensed view of FIGS. 4-7. At step A, an organic amine andan aldehyde, such as formaldehyde or paraformaldehyde, are combined(Liquid I). At step B, a hemiaminal low melting point gel is formed (GelI). At step C, the hemiaminal low melting point gel is changed to aliquid solution by the addition of an M(+III) complex (Liquid II).Iron(III) is shown for example. Using iron(III) as a catalyst andheating allows formation of a greater melting point gel at step D (GelII). The greater melting point gel at step D, comprising a triazinecore, can be returned to a liquid solution by the addition of excessiron(III), or by the addition of acid as discussed previously.

Heating the organometallic liquid described in Table 2 (Experiment II-A)reduces the gel time, or in other words the time it takes a greatermelting point gel to form from a liquid solution. Referring now to FIG.12, a graph is provided showing the time dependence of rheology for thegel formulation described in Table 2 at various temperatures. While ittakes about 90 hours to achieve a gel at 55° C., a gel is obtained inabout 6 hours at 87° C. (see FIG. 12). Another factor influencing thegel time is the relative concentration of NMP in the formulation. Thegel time was longer when 260 equivalents of NMP were used in theformulation (see Table 3 and FIG. 13) as opposed to 65 equivalents as inthe formulation presented in Table 2.

Referring now to FIG. 13, a graph is provided showing the viscosityversus time for a sample gel with 24.4 molecular equivalents of sodiumsulfite to JEFFAMINE® and showing a sample gel without sodium sulfite.The addition of sodium sulfite to the ferric hemiaminal liquidsaccelerates the formation of greater melting point triazine-based gels.When the liquid described in Table 3 was heated to 60° C., the liquidtransitioned to a gel in about 17.5 hours. From experiment II-B it hasbeen determined that the addition of 9.2 molecular equivalents (relativeto JEFFAMINE® T-5000) of sodium sulfite results in a significantshortening of the gel time to 12.5 hours. FIG. 13 depicts thistransition. Sodium sulfite therefore can be used as an accelerator totune the gel time of gel chemical system for producing greater meltingpoint gels.

Referring now to FIG. 14, a graph is provided showing the effect ofincreasing aluminum chloride content on gel time at 68° C. The data fromExperiment II-C is presented in FIG. 14. When the precursor hemiaminalliquid is heated to 69° C., the liquid transitions to a gel in about 2.0hours. The addition of 6.8 molecular equivalents (relative to JEFFAMINE®T-5000) of aluminum chloride hexahydrate results in a significantlengthening of the gel time to 3.5 hours. Therefore, on one handaluminum(III) acts as a catalyst for the formation of the triazine gelbut on the other hand it acts as a retarder. The more aluminum that isadded, the slower the transformation to the triazine, after a certainpoint.

Aluminum chloride acts as both an accelerator to gel formationcatalyzing formation of a triazine complex, and as a retarder bystabilizing reactants prior to the triazine product. Without being boundby any theory or principle, the action of aluminum chloride is believedto occur because a trivalent metal (or “M(+III)”) lessens the activationenergy for the ring closing of product G to product H (discussed withregard to FIG. 1B). An M(+III) also stabilizes liquid by binding toanyone of the structures from A to F in FIGS. 1A and 1B. Thisstabilization retards the formation of product H because the relativeactivation energy is increased by the lessening of the free energies ofthe structures (A-F) responsible for the liquid state.

In some embodiments, ferric ammonium sulfate accelerates the formationof the triazine, but the addition of increasing amounts of ferricammonium sulfate to the solution also leads to a decrease in the rate offormation of triazine. This may occur through the same mechanism as theretardation of the product formation in the case of aluminum.

Referring now to FIG. 15, a graph is provided showing the effect ofincreasing ferric ammonium sulfate concentration on gel time at 69° C.Experiment II-D is the iron(III) analogue to Experiment II-C. InExperiment II-D, increasing the amount of iron(III) relative to the 65:5hemiaminal organometallic liquid also increases the gel time. Theresults for Experiment II-D are graphed in FIG. 15.

Referring now to FIG. 16, a graph is provided plotting the relative geltimes for hemiaminal gels complexed with aluminum(III) and iron(III).Comparing the gel times of the iron(III) and aluminum(III) gels shows asubstantial increase in the gel time for gels prepared with iron(III).Iron(III) is a more strongly retarding additive to triazine greatermelting point gel formation. FIG. 16 shows the difference graphically ina linear plot of gel time to M(+III) concentration. Regardless of theirrelative differences in terms of retarding effectiveness, they bothdisplay this propensity to retard gel formation with increasingconcentration.

Aluminum(III) acts as a catalyst for triazine gel formation. Triazinegel formation is faster with 1.1 equivalents of ARM) than in the absenceof a trivalent metal additive. Results from Experiment II-E show that a65:5 hemiaminal gel was heated to 120° C. (past the melting point of thegel) and analyzed with a Grace Instruments rheometer in oscillatoryshear mode (1 Hz and 10% strain).

Referring now to FIG. 17, a graph is provided showing storage modulusand loss modulus results at 72° C. and 115° C. for the results ofExperiment II-E. The cross-over point for the storage and loss modulifor the hemiaminal liquid in the absence of M(+III) at 115° C. occurs atabout 8.25 hours (point A), whereas the cross-over point for the storageand loss moduli for the same gel digested with 1.1 equivalents ofaluminum(III) occurs at just over an hour at 72° C. (see point B). Thiscross-over point can be considered as the point where the liquidtransforms into a gel. The storage and loss moduli at 25.6° C. are 632Pascals (“Pa”) and 0 Pa, respectively. The storage and loss moduli at77.8° C. are 685 Pa and 0 Pa, respectively. The storage and all modulusvalues were obtained at 1 Hz with 10% strain. The triazine gelation timeof a 65:5 hemiaminal fluid at 115° C. is about 8.3 hours. The storageand loss moduli at 25.0° C. are 1.020 kilopascals (“kPa”) and 0 kPa,respectively. The triazine gelation time of a 65:5 hemiaminal fluid with1.1 equivalents of AlCl₃ at 72° C. is about 1.1 hours.

While Gel II, depicted in FIG. 10, can be accessed through complexationwith M(+III), Gel II is also accessed in the absence of M(+III). Al(III)hastens the formation of Gel II, but the more Al(III) that is added pasta certain point, the slower the conversion becomes.

Referring now to FIGS. 18 and 19, FIG. 18 provides a graph showinggelation time of a 65:5 gel with 1.2 equivalents of AlCl₃ by showingincrease in modulus over time. FIG. 19 is a graph showing the cross-overpoint A of the storage modulus and the loss modulus at about 120° C. forthe sample of FIG. 18.

Additive Release from Hemiaminal Gels

Referring now to FIGS. 20-23, in a first experiment for Additive Releasefrom Hemiaminal Gels, the gel formulation described in Table 8 wastested for timed release activity. JEFFAMINE® ED900 is a polyethyleneglycol diamine with a molecular weight of about 900 Da, and was obtainedfrom Huntsman International LLC. LOMAR® D, produced by GEO SpecialtyChemicals, is used as an oil well cement disperant and has a signaturein the UV range (with a broad absorption peak at about 300 nm) that isuseful in the determination of the disintegration of gels and therelease of a gel's contents. The gel was produced by heating theformaldehyde with NMP at 60° C. for 40 minutes and then adding theremaining contents and stirring for 30 minutes. The gel appeared to behomogenous. The ultraviolet-visible (UV/VIS) spectrum study of therelease of the contents of a gel of LOMAR® D was studied by taking a 1.5gram sample of the gel and placing it in 90 grams of solvent.

In a first test, the solvent was water. In a second test, the solventwas NMP. In a third test, the solvent was 10 grams of AlCl₃ dissolved in90 grams of NMP. In each of these tests for the Additive Release fromHemiaminal Gels Experiment, the baseline was set as the solvent prior tothe addition of the gel. Then, the breakdown of the gel was measured bya change in the spectra as a function of time.

TABLE 8 Formulation of a polyethylene glycol based hemiaminal gel forthe first Additive Release from Hemiaminal Gels Experiment. MaterialMolecular Weight Mass (g) Moles Molar Ratio Ratio Formaldehyde 30.031.04 0.034632 2.308802309 1 JEFFAMINE ® 900 13.5 0.015 1 0.433125 ED900NMP 99.13 21.1 0.212852 14.19012072 14.19012 LOMAR ® D 0.5

FIG. 20 is a graph showing time resolved UV/VIS spectra for the releaseof LOMAR® D and the disintegration of the hemiaminal gel in water. After2 hours, the gel had completely disintegrated and was no longer visiblein the liquid.

FIG. 21 is a graph showing time resolved UV/VIS spectra for the releaseof LOMAR® D and the disintegration of the hemiaminal gel in NMP. After24 hours, the gel appeared to be still intact within the liquid. FIG. 22is a graph showing time resolved UV/VIS spectra for the release ofLOMAR® D and the disintegration of the hemiaminal gel in NMP with AlCl₃.As can be noted from FIGS. 20-22, the gel responds differently todifferent solvent environments.

The polyethylene-glycol based gel is sensitive to the presence of waterand disintegrated quickly in water (within 2 hours all the gel haddisappeared). (This was not the case when the gel was a polypropyleneglycol based hemiaminal gel, such as with JEFFAMINE® T-5000). When thetested gel was placed in NMP (FIG. 21), there was no appreciabledisintegration of the gel over periods of hours to days at roomtemperature. FIG. 22 shows the effect of AlCl₃ dissolved in the NMP.This caused the gel to disintegrate rapidly. The particulates caused bythe disintegration result in increased light scattering. This can beseen in the plot in FIG. 22, as the background from 800 nm to 300 nmincreases with time. Observation of the sample also indicated thatparticulates would be produced in the solvent as the gel wasdisintegrating. After about 5 hours, the gel in NMP with AlCl₃ hadcompletely disintegrated and was no longer visible in the liquid.

In a second experiment for Additive Release from Hemiaminal Gels withN-vinyl pyrrolidone (“NVP”) copolymerized with N-butyl acrylate, the gelformulation described in Table 9 was tested for timed release activity.JEFFAMINE® ED900 is a polyethylene glycol diamine with a molecularweight of about 900 Da, and was obtained from Huntsman InternationalLLC. The gel was produced by heating the formaldehyde with NVP at 60° C.for 40 minutes and then adding N-butylacrylate, potassium persulfate,LOMAR® D and stirring for 30 minutes. The solid rendered from thisexperiment appeared to be homogenous. The UV/VIS study of the release ofLOMAR® D from the gels was studied by taking a 1.5 gram sample of thegel and placing it in 90 grams of water.

As may be noted from FIG. 23, the release profile for NVP/N-butylacrylate polymer-hemiaminal system in water is substantially differentfrom that of the NMP hemiaminal gel in water, shown in FIG. 22. TheNVP/N-butyl acrylate polymer (FIG. 23) clearly inhibits the release ofLOMAR® D. More than ten times the amount of polymer is released from theNMP gel (FIG. 22) than from the copolymer system after an hour at roomtemperature in de-ionized water.

TABLE 9 Formulation of a polyethylene glycol based hemiaminal gel for asecond Additive Release from Hemiaminal Gels Experiment. MolecularMaterial Weight Mass (g) Moles Molar Ratio Ratio Formaldehyde 30.03 1.040.034632 2.308802309 1 JEFFAMINE ® 900 13.5 0.015 1 0.433125 ED900 NVP111.14 23.65637 0.212852 14.19013333 6.146102 N-butyl acrylate 128.1727.28124 0.212852 14.19013333 6.146102 Potassium Persulfate 270.322 0.250.000925 0.061654866 0.026704 LOMAR ® D 0.5

While downhole pH values can vary, water-based drilling fluids typicallyrange from about pH 8 to about pH 12. Oil well cement is typically of apH between about pH 10 and about pH 11.5. In the case where the gels ofthe present disclosure are introduced to water-based drilling fluids,the stability of the gel can be tested in the presence of the drillingfluid for compatibility by one of ordinary skill in the art.

In embodiments of the present disclosure, the reversible aminal gelsdisclosed can be used in compositions, systems, and methods forextracting hydrocarbons from hydrocarbon-producing reservoirs. In someembodiments, delayed acid precursors such as polyester, polylactic acid(“PLA”), and polyglutamic acid (“PGA”), for example, can be consideredto reverse the gel when it is required to remove the gel as a liquid,for example in the application of temporarily plugging a well.

Gel Time Experiments for the Transformation of Gels from Hemiaminal toTriazine-Based Gels with Tri-Aminated Polypropylene Glycols Tested withSmall Amplitude Oscillatory Shear

Rheological measurements were performed on an Anton Paar MCR 302Rheometer equipped with a Peltier heater and an overhead hood forconvective temperature regulation. The measuring system was a titanium25 millimeters (“mm”) parallel plate measuring system (PP-25 Ti). Forall of the melting point determinations, the gels were placed on thestage and melted at a temperature slightly higher than the measuredmelting point so that they conformed to the geometry of the parallelplates once the plates are 1 mm apart from one another.

Melting points determined with the Anton Paar MCR 302 were observed witha temperature ramp rate of 2° C. per minute. This rate was determined tobe the optimum ramp rate for the gels, balancing the thermalconductivity of the compositions with the observed propensity for thefluids to transform into the thermodynamically favored closed-ringtriazine.

Certain gels that are kinetic (see, for example, FIGS. 1A-1B, A-G) andnot thermodynamic products (see, for example, FIG. 1B, H), so a slowerramp rate could affect the results and artificially raise the measuredmelting point as the gel slowly converts into the thermodynamic ringclosed triazine product (see, for example, FIG. 1B, H). Two degreesCelsius per minute is the fastest ramp rate that ensures that the sampleis at the temperature of the base plate of the parallel plates,providing the heating. Gelation times were measured in the Anton PaarMCR 302 operating in oscillatory mode at a frequency of 1 Hz and astrain amplitude of 1%. All gel times measured through this method wheremeasured at 70° C.

The method for synthesizing the hemiaminal gels was as follows:JEFFAMINE® T-5000 was added to formaldehyde in NMP. JEFFAMINE® T-5000 isa tris primary amine of polypropylene glycol with an approximatemolecular weight of 5000 Da. To prepare the hemiaminal gels,paraformaldehyde was added to NMP and stirred for 30 minutes at 60° C.Then an amount of JEFFAMINE® T-5000 was added to the NMP solution andstirred for 20 minutes at 60° C.

In experiments where NH₄(Fe(II))SO₄ was added, 0.2 grams of Fe(II) wasadded directly to the newly formed hemiaminal molten gel prior toremoving from heat. After the addition of the ferrous compound, thesample was removed from the heat and stirred until homogeneous whilecooling to room temperature. For samples where the addition of trivalentmetal salts was examined, the gel formed from the condensation offormaldehyde and JEFFAMINE® T-5000 in NMP was broken down through theaddition of an Fe(III) or Al(III) complex. In order to hasten thecomplexation of metal in the material, the gel was sliced into smallpieces to increase the surface area for reaction with the metal salt.

The amount of JEFFAMINE® added to the solution was varied to demonstratethe effect of the change in amine to aldehyde concentration from anamine to aldehyde ratio of 0.55 to 1.7. These samples are labeled A-1through A-5 in Table 10. Table 1 describes the proportions of thecomponents in the tested gel. The mixing of the materials here is alsoreferred to as General Chemical Method I.

TABLE 10 Formulations for the different samples for Gel Time Experimentsfor the Transformation of Gels from Hemiaminal to Triazine-based Gelswith Tri-aminated Polypropylene Glycols tested with small amplitudeoscillatory shear. Variable amine:aldehyde ratio with a formaldehydeconcentration of 0.216M. Mass of JEFFAMINE ® JEFFAMINE ® T-5000Amine:Aldehyde Sample T-5000 (g) (millimoles) Ratio A-1 4.0 0.8 0.55 A-26.0 1.2 0.83 A-3 8.0 1.6 1.1 A-4 10 2.0 1.4 A-5 12 2.4 1.7

As a comparison point, a parallel set of gels was made of A-1 to A-5where 0.2 grams of NH₄(Fe(II))SO₄ was added prior to cooling the gel inthe process of the hemiaminal synthesis described in General ChemicalMethod I.

Experiments for Gel Destruction and Reformation with Aluminum Chloride

Gels produced through the condensation of formaldehyde and polypropyleneglycol amine can be transformed into liquids through the addition of atrivalent metal. In this experiment, the effect of aluminum chloridehexahydrate is studied as a function of concentration of gels ofidentical composition. After the gel is reverted to a liquid, it is thenheated to observe the second gelation time of the material. Thesetransitions were examined rheologically with temperature and smallamplitude oscillatory shear (“SAOS”) experiments. The most commonapproach for measuring time-dependent viscoelastic properties of amaterial on a rotational rheometer is to perform small amplitudeoscillatory shear over a range of oscillation frequencies

The formaldehyde concentration was 81.7 millimole (“mM”) in NMP with anamine to aldehyde ratio of 0.55. The amount of aluminum chloride addedto the solution was varied to demonstrate the effect of the change intrivalent metal concentration on the gelation of the liquid. Thesesamples are labeled B-1 through B-4 in Table 12. After the addition ofaluminum to the hemiaminal gels and following the transformation of thematerials into liquids, the gel times of the materials were observed at70° C. in a rheometer set to measure at fixed frequency (1 Hz) andamplitude (0.1% strain) in SAOS mode.

TABLE 11 Formulation for initial hemiaminal gel in Experiments for GelDestruction and Reformation with Aluminum Chloride. Material Molar RatioMass (grams) Moles Paraformaldehyde 5.4 1.04 0.0346 JEFFAMINE ® T-5000 132.0 0.0064 N-Methyl pyrrolidone 64.9 41.2 0.4155

TABLE 12 Varying amounts of aluminum chloride added to initialhemiaminal gels. Molar Ratio to Mass of Moles of Sample JEFFAMINE ®T-5000 AlCl₃•6H₂O (g) AlCl₃•6H₂O B-1 1.13 1.75 0.00725 B-2 1.46 2.250.00932 B-3 1.94 3.0 0.0124 B-4 2.27 3.5 0.0145Experiments for Demonstration of the Effect of Aluminum ChlorideConcentration on the Gelation Time.

The effect of aluminum chloride was examined in this experiment. Asshown in the formulation in Table 13, increasing amounts of aluminumchloride were added to the 65:5 hemiaminal gel. This gel had acomposition with amine to aldehyde molar ratio of 0.55 and aformaldehyde concentration of 0.865 M. For each of these threecompositions with differing concentrations of aluminum chloridehexahydrate, the gelation time is measured at a temperature of 68° C.

TABLE 13 The formulations examined in Chemical Method II (as describedfurther as follows). Amine to aldehyde molar ratio of 0.55 at aformaldehyde concentration of 0.865M. Molar Mass Material Ratio (grams)Moles Paraformaldehyde 5.4 2.08 0.0692 Jeffamine T-5000 1 64.0 0.0128N-Methyl pyrrolidone 64.9 82.4 0.831 Aluminum Chloride 1.2, 4.1, 3.8,12.7, 0.0157, 0.0526, Hexahydrate 7.0 21.6 0.0895Experiments for Gel Destruction with Ferric Ammonium Sulfate

The gels, A-1 through A-5, were reacted with ferric ions in the form offerric ammonium sulfate, whereby ferric ammonium sulfate was added inthe amount of 0.51 millimoles (“mmoles”) (0.246 g) to render the ferricto JEFFAMINE® T-5000 ratio to be 0.63, 0.42, 0.32, 0.25, and 0.21 forsamples A-1 through A-5, respectively.

Experiments for the Demonstration of the Effect of Ferric AmmoniumSulfate as a Catalyst and a Retarder for Triazine Ring Closure

As in the Experiments for Demonstration of the Effect of AluminumChloride Concentration on the Gelation Time, the gel examined forExperiments for the Demonstration of the Effect of Ferric AmmoniumSulfate as a Catalyst and a Retarder for Triazine Ring Closure has acomposition with amine to aldehyde molar ratio of 0.55 and aformaldehyde concentration of 0.865 M. The effect of iron(III)concentration on the gelation time was observed in this experiment.Varying amounts of iron(III) were added to the hemiaminal gel asdescribed in Table 14. The gelation times are measured at 68° C.

TABLE 14 Varying amounts of iron(III) were added to the hemiaminal gelas shown. Material Molar Ratio Mass (grams) Moles Paraformaldehyde 5.42.08 0.0692 JEFFAMINE ® T-5000 1 64.0 0.0128 N-Methyl pyrrolidone 64.982.4 0.831 Ferric Ammonium 1.1, 1.5, 6.8, 9.25, 11.7, 0.014, 0.019,Sulfate Dodecahydrate 1.9, 5.2 32.1 0.024, 0.067General Chemical Method II. The Addition oftris(2-carboxyethyl)phosphine to Triazine

Certain experiments tested triggered release from a triazine gel. Inother words, “cracking open the ring” was tested, for example, by theaddition of phosphine to aluminum aminal gels. 3.01 grams of liquid,B-1, was heated to 70° C. for 2 hours. Then, 1.38 grams oftris(2-carboxyethyl)phosphine was added to the gel along with 2 grams ofN-methyl pyrrolidone. The material was stirred for three days. Afterthree days it was dissolved. The shear modulus of B-1 was compared ateach of these steps.

TABLE 15 Gel formulations for the different “A” samples. Mass ofJEFFAMINE ® Hemiaminal JEFFAMINE ® T- Hemiaminal to Aminal at T- 5000Amine:Aldehyde Measured Melting 110° C. Sample 5000 (g) (mmoles) RatioPoints (° C.) (min) A-1 4.0 0.8 0.55 51.1 206 A-2 6.0 1.2 0.83 73.1 n/aA-3 8.0 1.6 1.1 105.5 192 A-4 10 2.0 1.4 79.4 230 A-5 12 2.4 1.7 68.0276

Table 15 summarizes the melting points and hemiaminal to triazineconversion rates of the formulations A-1 through A-5. Through thesesamples, the amine (from JEFFAMINE® T-5000) to aldehyde ratio isadjusted from 0.55 to 1.7. The melting points of the hemiaminal gels (A1through A5) are observed to vary as a function of the amine to aldehyderatio. FIG. 24 plots this relation. The highest melting point isobserved for the amine to aldehyde ratio of about 1:1, likely, withoutbeing bound by any theory or principle, because this ratio offers themaximum number of aldehyde reacted amine to free amine while ensuringthe minimum amount of reduction in the free amine ends in a polymerchain. Ultimately, in certain embodiments, the triazine (thermodynamicproduct) requires a 1:1 amine to aldehyde ratio to be optimized. Otherratios may reduce the branch density of the polymer network.

Referring now to FIG. 24, the melting point trend is shown as a functionof amine:aldehyde ratio for gels produced through the method describedin this section. For all gels tested, JEFFAMINE® T-5000 was used as theamine, and the molar concentration of formaldehyde in NMP was 0.216 M.

When Mohr's salt (ammonium iron(II) sulfate hexahydrate) was added tothe gels in the synthesis of the gels, the melting points were reducedfrom their values in the absence of iron(II) with the exception of A-5which increases by 0.5° C. Furthermore, the presence of iron(II) appearsto catalyze the formation of the triazine structure from the openhemiaminal structure. All gels that are converted to the triazine ringsstructures have melting points in excess of 200° C., which is the hightemperature limit of the Anton Paar MCR 302.

TABLE 16 Samples A-1 through A-5 prepared with 0.2 g of Mohr's salt.Fe(2) Hemiaminal Mass of JEFFAMINE ® Measured JEFFAMINE ® T-5000Amine:Aldehyde Amine:Fe(II) Melting Points Sample T-5000 (g) (mmoles)Ratio ratio (° C.) A-1 4.0 0.8 0.55 0.64 49.0 A-2 6.0 1.2 0.83 0.43 56.5A-3 8.0 1.6 1.1 0.32 61.4 A-4 10 2.0 1.4 0.26 63.4 A-5 12 2.4 1.7 0.2168.5

Referring now to FIGS. 25A-H, the amplitude sweeps of samples A-1through A-4 are shown. The rheology of the gels was tracked as shown inFIGS. 25E-H to ensure that the gels were stabilized and showed minimalchanges in storage and loss moduli prior to beginning the amplitudesweeps (in FIGS. 25A-D). FIGS. 25E-H show stabilization of gelrheological properties after temperature stabilization at 25° C. for A-1(FIG. 25E), A-2 (FIG. 25F), A-3 (FIG. 25G), and A-4 (FIG. 25H).

Samples A-1 through A-4 were swept for amplitude, and the results areshown in FIGS. 25A-D. The gels each had a different stiffness anddifferent response to amplitude changes. In particular, sample A-3 inFIG. 25C showed a shorter linear region in the amplitude sweep than theother gels. In sample A-3, the loss modulus increased to significantlygreater than a shear strain of about 0.5. The other gels were linearthrough to at least a shear strain of about 1.0.

Gel samples A-1 and A-4 in FIGS. 25A and 25D, respectively, showed thelargest linear region. Of interest is the effect of iron(II) on thesweep amplitude profile of the gels. The addition of ferrous ammoniumsulfate has the effect of increasing the strain tolerance for the gelsA-1 through A-5. The effect of iron(II) is shown in FIG. 26. FIG. 26A isa graph showing phase shift angle versus shear strain for sample A-5,sample A-5 with 0.2 grams of Mohr's salt, and sample A-5 with 0.8 gramsof Mohr's salt. FIG. 26B is a graph showing phase shift angle versusshear strain for sample A-3 and sample A-3 with iron(II), along withamplitude sweep and corresponding phase angle.

The case of adding iron(II) is distinct from the case where iron(III)was added to the gels. When a ferric iron(III) salt was added to thegels A-1 through A-5, the gels reverted back to a liquid. FIGS. 27A and27B show photographs of the gels after the addition of ferric ammoniumsulfate. The A-1 gel showed the fastest and most complete conversion toliquid accompanied with a color change to red. FIG. 27A is a pictorialrepresentation of the addition of a trivalent metal salt, ferricammonium sulfate, to samples A-1 through A-5. FIG. 27B is a pictorialrepresentation of the addition of a trivalent metal salt, ferricammonium sulfate, to samples A-1 through A-5.

Referring now to FIG. 28, when sample A-1 was reacted with aluminumchloride the gel turned to a liquid, as shown in FIG. 28A. When sampleA-1 was heated to 70° C., it is transformed back to a gel state, asshown in FIG. 28B. The gel was then broken down back to a liquid throughthe addition of phosphine in NMP, as shown in FIG. 28C.

The time of the transformation of the liquid in FIG. 28A to the gel inFIG. 28B depends not only on the temperature but also the concentrationof aluminum in the sample. FIGS. 29A and 29B show the results of a smallamplitude oscillatory rheometry experiment in which different amounts ofaluminum chloride were added to the same gel composition and theresulting gel time for the organometallic liquid at 70° C. was recorded(FIG. 29B). Increasing amounts of aluminum chloride increase the geltime.

In the state of the art, many completion fluids which are designed tobuild up viscosity or form reversible gels suffer from performancelimitations due to thermal degradation of the fluids and gels attemperature conditions of many oil and gas wells. Manycommercially-available fluids begin to thermally degrade at temperaturesgreater than about 50° C. Current screen running kill pill formulationsavailable in the industry are based upon biopolymer, xanthan,cross-linked starch, and guar formulations which suffer from seriouslimitations in performance.

With average hydrocarbon-bearing reservoir temperatures of approximately140° C., mechanical packers are often required in place of fluidformulations for screen running. This leads to greater expense andpotential formation damage. Thus, there is a need for higher temperaturekill pills than those commercially available. High temperature drillkill pills of the present disclosure have utility across open-holecompletions and plug and perforate operations. These formulations arestable as solid gels at and greater than about 140° C. for a period oftime, for example between about 1 hour and 1 week.Constitutionally-dynamic reversible aminal gels described here arestimulus-responsive materials, which can be advantageously used as hightemperature “kill pills” in some embodiments. As used here, “kill pill”refers to materials that can stop flow of fluids in a wellbore orreservoir environment.

Hemiaminal/aminal metallogel compositions and systems disclosed andexemplified here demonstrate performance without degradation attemperatures up to about 150° C. and pressures up to about 60 MPa.Chemical systems also demonstrate reversibility under stimulated wellconditions whereby thermodynamically favored metallogels can be broken,or returned to a liquid fluid state, within a sandstone core samplepressurized at 3.4 MPa and held at 70° C. These findings exemplify thesuitability of these reversibly covalent chemical systems ashigh-performance completion fluids for such operations as perforationsand workovers.

Hemiaminal (Kinetic) Gel Preparation Procedure

N-methyl pyrrolidone (NMP) and paraformaldehyde (in the proportionsdescribed in Table 17) were mixed together at 70° C. in an oil bath on aheated stir plate for 30 minutes. A polyoxypropylene triamine(trifunctional primary amine) with a molecular weight of 5 kiloDaltons(JEFFAMINE® T-5000 from Huntsman Corporation) was then added to themixture and allowed to continue to stir at 70° C. for another 30minutes. The pH of the product of this reaction was measured at about pH7-8. The mixture was then removed from the oil bath and allowed to coolto room temperature where a gel formed, referred to here as a “65-5kinetic gel” (A in FIG. 30).

Transformation of the Hemiaminal (Kinetic) Gel to Liquid Phase

The prepared hemiaminal kinetic gel was next cut into smaller pieces andplaced into a jar with a magnetic stir rod. Aluminum chloridehexahydrate in the amounts indicated in Table 17 were added into the jarwith the pieces of gel and allowed to stir for 24 hours, where breakdownof the gel into liquid occurred, producing what is referred to here as a“65-5 liquid” (B in FIG. 30). The pH of the liquid was measured at aboutpH 6.

TABLE 17 65-5 Kinetic Gel and 65-5 Liquid Formulations with NMP. MolarRatio to Weight JEFFAMINE ® T- Material (g) 5000 MolesN-methyl-2-pyrrolidone (NMP) 41.2 64.9 0.416 Paraformaldehyde 1.04 5.40.0346 JEFFAMINE ® T-5000 32.0 1 0.0064 Aluminum Chloride 1.85 1.20.0077 HexahydrateRheology Experiments

The 65-5 liquid (from the ratio of NMP to paraformaldehyde where theratio of paraformaldehyde to JEFFAMINE® T-5000 is 5.4:1) was tested in aGrace M5600 high pressure high temperature (HPHT) rheometer to study thetemperature effects on gelation time at 3.4 MPa. The rheometer uses anoscillatory test where the sample is subjected to a steady 1 Hzfrequency and 100% amplitude oscillatory strain. The resulting stress ismeasured and recorded as an elastic and viscous modulus (G′ and G″respectively). Gel time is interpreted as when G′ crosses over G″. Thesystem was tested at 70° C., 100° C., and 150° C. (results shown in FIG.31).

The 65-5 liquid was tested in a Fann i-X77 HPHT rheometer to study theeffect of varying pressure on gelation time while holding the sample ata constant 70° C. A rotational sweep program was used to simulateoilfield testing conditions and to establish a gel time under 20, 35,and 60 MPa (results in FIG. 32). Initial increases in shear stress showtime for gelation.

Core Flood Experiment

Core flood testing was conducted in a Grace 9100 Core Flow apparatus. Toprepare the core for the gel breaking study, an Idaho Gray sandstonecore (6 inches in length, 1 inch in diameter) was vacuum pumped for 2hours in the 65-5 liquid from above to saturate the pores in the core.The core was removed from the vacuum pump apparatus, fully submergedwith excess 65-5 liquid and placed into an oven at 70° C. overnight,where the liquid solidified into a gel over time. After allowing thegelled core to cool to about room temperature, excess solidified gel wasremoved from the exterior of the core, and a fully-saturated, gelledcore was left for testing.

The accumulator in FIG. 33, discussed further as follows, holds eitherneat NMP or a saturated solution of 50 g ofTris(2-carboxyethyl)phosphine (“TCEP”) dissolved in 500 mL of NMP,depending on the experiment.

Gel Weighting Procedure

The density of example compositions for use as a kill pill can beadjusted with the addition of salts. Density adjustments can be madewith, for example, zinc bromide and sodium bromide. Zinc bromideprovides an advantageous density at 1.35 grams/cubic centimeter(“g/cc”), and sodium bromide achieves about 1.1 g/cc. Sodium bromidealso offers advantageous temperature stability. The method of densityadjustment with salt follows, and shown is an example case for zincbromide.

Zinc bromide is added to NMP stirring at room temperature until a fullysaturated solution of ZnBr₂ in NMP is achieved. The proportions aredescribed in Table 18. The density of the fully saturated solution isabout 1.35 g/cc as measured by a pycnometer.

The ZnBr₂ saturated NMP and paraformaldehyde are mixed together at 70°C. in an oil bath on a heated stir plate for 30 minutes. JEFFAMINE®T-5000 was then added to the mixture and allowed to continue to stir at70° C. for another 30 minutes. The mixture was then removed from the oilbath and allowed to cool to room temperature where a gel would form.

TABLE 18 Weighted Sample Formulations with Example Salt. Molar Ratio toJEFFAMINE ® T- Material Weight (g) 5000 Moles NMP Saturated with ZnBr₂41.2 64.9 0.416 Paraformaldehyde 1.04 5.4 0.0346 JEFFAMINE ® T-5000 32.01 0.0064

A schematic for the chemical transformations in the dynamic covalentsystems studied is presented in the reaction scheme of FIG. 30. This issimilar to the schemes shown in FIGS. 3 to 7. The chemical systeminvolves the condensation of a polypropylene glycol triamine withformaldehyde in the polar aprotic solvent, N-methyl pyrrolidone (NMP).FIG. 30 shows the condensation of a functionalized amine where the R—NH₂group corresponds to an alkylene glycol triamine.

Different products are denoted by letters A, B, C, and D, and correspondto different chemical structures and material phases. The initialcondensation involves a number of intermediates in the process of theformation of product B, which have been abbreviated in FIG. 30. Thedynamics of the condensation are modified through the addition of atrivalent metal salt (M(III)), such as aluminum chloride, in addition toor alternative to another metal salt, such as zinc bromide or sodiumbromide (M(II)). The addition of the trivalent metal has the effect ofreversing the initial kinetic hemiaminal gel to a liquid (A to B of FIG.30), such that the earlier products in the condensation pathway arefavored over the final products at room temperature. The resultingorganometallic liquid with the trivalent metal can be transformed into amore thermodynamically stable gel with heating (B to C of FIG. 30). Thisgel can in turn be reverted to liquid with the addition of TCEP in NMP(C to D of FIG. 30) (or alternatively with NMP).

Demonstrating that the hemiaminal chemistry can be weighted with saltscommonly used in the oil field, zinc bromide has been shown here to workas a good density modifying agent. Weights of up to about 1.35 g/cc arepossible with the liquids loaded in this way.

As shown in FIG. 31, when pressure is increased and held constant andtemperature is varied, there is a similar correspondence observed as waspreviously observed under atmospheric pressure conditions. A rise intemperature leads to a faster rate of gelation. Specifically, when the65-5 liquid is maintained at 3.4 MPa and heated to 70, 100, and 150° C.,the corresponding gel times, measured from the elastic and viscousmodulus cross-over are 340, 190 and 40 minutes, respectively.

These results correspond with what has been previously observed andreported under atmospheric pressure. That the transformation occurs attemperatures up to 150° C. indicates, in part, the suitability for thischemical system under higher temperature wellbore situations. Thetemperature dependence of the gelation time at 3.4 MPa is displayed inFIG. 31, and the data presented in FIG. 31 are from small amplitudeoscillatory shear experiments where G′ is the elastic modulus of thematerials tested and G″ is the viscous modulus. The 65-5 liquid(described in the experimental section) was heated to the threedifferent temperatures at 3.4 MPa, simulating three different wellboreenvironments. The data clearly show a decrease in gel time withincreasing temperature.

When the 65-5 liquid (B in FIG. 30) is heated to 70° C. and pressurizedto 20, 35 and 60 MPa, there is a pressure effect on the gelationkinetics. The gelation time displays a pressure dependence such that anincrease in pressure decreases the gel time. At 20, 35, and 60 MPa, thecorresponding gel times observed are 390, 270 and 140 minutes,respectively. The measurements indicate that the pressure acceleratedthe formation of the species towards the end of the condensationpathway, where formaldehyde and the trifunctional amine, JEFFAMINE®T-5000, condense increasingly branch hemiaminal and aminal condensationproducts. As shown in FIG. 32, the 65-5 liquid (described in theexperimental section) is heated to 70° C. at three different pressures,simulating three different wellbore environments.

Referring now to FIG. 33, core flooding designs are illustrated and showthe pathway for NMP and NMP/TCEP solutions to break the thermodynamic65-5 gel formed and plugging an Idaho sandstone core. In system 3300,NMP or NMP/TCEP is poured into the top reservoir 3301 of the accumulator3302. The ISCO pump 3304 uses DI water 3306 from DI water reservoir 3305and line 3303 to push the piston 3308 in the accumulator 3302 upwardly,creating flow of the NMP solution through line 3310. The ISCO pump 3304also controls the flow rate/set pressure of the NMP solution as itbuilds up on the bottom of the gel saturated core 3312 and reads out asbottom pressure 3316. The gel saturated core 3312 has 6.8 MPa confiningpressure applied in the core holder 3313. Flow in line 3314 indicatesthe flow of breakthrough from the experiment with NMP or the experimentcontaining NMP and TCEP. When the top pressure reading 3318 matches thebottom pressure reading 3316, breakthrough is assumed to have occurred.

FIG. 34 is a graph showing the results of testing of the gel breakingability of TCEP in a Grace 9100 Core Flow apparatus. As shown, toppressure rises quickly (in other words breakthrough occurs quickly)using a combination of NMP and TCEP to break the gel. FIG. 34 shows theoutput of the top pressure 3318 from the sample core 3312. The toppressure 3318 is measured as a function of time with the bottom pressure3316 being ramped to the point of fluid breakthrough. The experimentdemonstrates that the TCEP does degrade the gel in the core 3312 toallow for the return of free passage with no damage to the core sampleobserved, suggesting no formation damage from the use of thesematerials. The breakdown to the gel with TCEP occurs, at least in part,through the nucleophilic attack of phosphine at the methylene carbon onthe aminal functional groups of the gels.

The stability of final formed thermodynamic 65-5 hexahydrotriazine gelsat temperatures at or greater than 150° C. depends, in part, on the saltused for complexation. Table 19 lists the stabilities observed forpolyhexahydrotriaziane gels (PHT Gels) for 1 hour, 24 hours, 3 days, and7 days. All of the gel systems listed in Table 3 display stability for24 hours; however, only the sodium bromide gel system shows enhancedstability for one week at 150° C.

TABLE 19 The thermal stabilities of different 65-5 PHT gels with metalsalts. Poly- Gel Stability at 150° C. Salt Catalyst hexahydrotriaziane 124 3 7 Used (“PHT”) Gel at 70° C. Hour Hours Days Days No Salt Yes Non/a n/a n/a Aluminum Yes No n/a n/a n/a Chloride Hexahydrate CalciumBromide Yes No n/a n/a n/a Cesium Chloride Yes No n/a n/a n/a ZincBromide Yes Yes No n/a n/a Calcium Chloride Yes Yes Yes No n/a DihydrateCalcium Chloride Yes Yes Yes No n/a Hexahydrate Sodium Bromide Yes YesYes Yes Yes

Hemiaminal/aminal metallogel systems have been demonstrated to performunder pressures up to 60 MPa and temperatures up to 150° C. Anadvantageously thermally stable gel formulation uses sodium bromide saltto extend this performance at 150° C. to one week. This extends theperformance window of the system to many conditions in oil and gas wellswhere currently-used high performance completion fluids show significantlimitations in operability. Increasing either the temperature or thepressure in these systems increases the reaction rate and drives theformation of the thermodynamically favored gel. Weighting of the gelwith zinc bromide is also demonstrated for situations where matching thepore-pressure within the rock formation with fluid hydrostatic pressureis desired.

In gelation tests where the gel systems were formed and stable at 70°C., the resulting gels were then immediately placed into a 150° C. ovento check for additional thermal stability. To check for stability, thevial containing said gel system would be flipped upside down and anymovement of gel in addition to or alternative to liquid would bevisually noted. A gel with no visual movement or liquid formation whileheld upside down is considered stable where as any other result iscalled unstable.

The reversibility inherent in the hemiaminal/aminal metallogels can beused to break the gels within a core sample under pressure in a standardcore flood apparatus. Tris(2-carboxyethyl)phosphine has been shown toeffectively break the gels within a highly permeable sandstone coresample. The breaking of the gel does not show remaining residue on thecore and is thus anticipated not to impart formation damage in rockformations where the completion fluid system is deployed. The gelbreaking in a core sample exemplified here is applicable to any of thestabilizing salts.

Fluids used when perforating are designed to prevent debris fromdegrading well equipment and limiting production. These fluids areusually brines which are weighted by the concentration of salt withinthe aqueous fluid. The salts range from potassium formate and calciumbromide to cesium formate, depending on the fluid density sought as wellas economic considerations.

During the perforation event, brines can often leak into the formationalong with debris and sand if the hydrostatic head of the fluid isgreater than the pore pressure of the reservoir rock (a situationreferred to as ‘overbalanced’). The density of the brines is oftenchosen to be overbalanced to prevent pore fluids from entering thewellbore during well construction operations. Since this situation canlead to losses of fluid into the formation, a secondary fluid typicallyreferred to as a fluid-loss control pill, or kill pill, is often placedacross the perforated interval to seal the perforations against furtherlosses which incur blockages through particle plugging and reaction withclays when present in the formation. This prevents the desired passageof oil and gas from the formation. In other well-bore cleaningapplications, and open hole completions, pre-packed liner fluid losspills are used in situations where oil production is stopped to cleanselected well zones from debris and particles limiting production. Thesetreatments are temporary, and all fluids and gels must be removed aftercleanup operations are completed. Kill pills therefore should also havezero formation invasion.

The singular forms “a,” “an,” and “the” include plural referents, unlessthe context clearly dictates otherwise. “Optionally” and its variousforms means that the subsequently described event or circumstance may ormay not occur. The description includes instances where the event orcircumstance occurs and instances where it does not occur. “Operable”and its various forms means fit for its proper functioning and able tobe used for its intended use.

In the drawings and specification, there have been disclosed embodimentsof compositions, systems, and methods for reversible aminal gels of thepresent disclosure, and although specific terms are employed, the termsare used in a descriptive sense only and not for purposes of limitation.The embodiments of the present disclosure have been described inconsiderable detail with specific reference to these illustratedembodiments. It will be apparent, however, that various modificationsand changes can be made within the spirit and scope of the disclosure asdescribed in the foregoing specification, and such modifications andchanges are to be considered equivalents and part of this disclosure.

Where the Specification or the appended Claims provide a range ofvalues, it is understood that the interval encompasses each interveningvalue between the upper limit and the lower limit as well as the upperlimit and the lower limit. The present disclosure encompasses and boundssmaller ranges of the interval subject to any specific exclusionprovided. Where the Specification and appended Claims reference a methodcomprising two or more defined steps, the defined steps can be carriedout in any order or simultaneously except where the context excludesthat possibility.

What is claimed is:
 1. A method for producing a reversible aminal gelcomposition for use as a kill pill, the method comprising the steps of:preparing a liquid precursor composition, the liquid precursorcomposition operable to remain in a liquid state at about roomtemperature, where the liquid precursor composition comprises: anorganic amine composition; an aldehyde composition; a polar aproticorganic solvent; and a metal salt composition; and allowing the liquidprecursor composition to transition from the liquid state to a gel statein situ proximate a hydrocarbon-bearing reservoir responsive to anincrease in temperature.
 2. The method according to claim 1, furthercomprising the step of returning the gel state to the liquid state insitu.
 3. The method according to claim 2, where the step of returningthe gel state to the liquid state comprises introducing aphosphine-containing compound to the gel state in situ.
 4. The methodaccording to claim 1, where the metal salt composition comprises a metalof valence 1, 2, 3, 4, or
 5. 5. The method according to claim 1, wherethe organic amine composition comprises a tris primary amine ofpolypropylene glycol with an approximate molecular weight of betweenabout 280 and about 100,000 Da.
 6. The method according to claim 1,where the organic amine composition comprises a bis primary amine ofpolyethylene glycol with an approximate molecular weight of betweenabout 200 and about 100,000 Da.
 7. The method according to claim 1,where the aldehyde composition comprises a compound selected from thegroup consisting of: formaldehyde, paraformaldehyde, phenolformaldehyde, resorcinol-formaldehyde, phenyl acetate-HMTA, and mixturesthereof.
 8. The method according to claim 1, where the polar aproticorganic solvent comprises a compound selected from the group consistingof: N-alkylpyrrolidone, N,N′-dialkylformamide, dialkylsulfoxide, andmixtures thereof.
 9. The method according to claim 8, where the polaraprotic organic solvent comprises N-methyl-2-pyrrolidone.
 10. The methodaccording to claim 1, where the metal salt composition comprises a metalselected from the group consisting of: iron(III), aluminum(III), andmixtures thereof.
 11. The method according to claim 1, where the gelstate comprises triazine-based molecules.
 12. The method according toclaim 1, further comprising the step of maintaining a stable gel statebetween about 100° C. and about 250° C. for between about 1 hour andabout 1 week.
 13. The method according to claim 1, further comprisingthe step of maintaining a stable gel state at about 150° C. for betweenabout 1 hour and about 1 week.
 14. The method according to claim 1,where a molar ratio of the organic amine composition to the aldehydecomposition to the polar aprotic organic solvent is between about 1:2:1and about 1:200:500.
 15. The method according to claim 1, furthercomprising the step of adjusting a ratio of components in the liquidprecursor composition to alter an amount of time required for a liquidhemiaminal gel form to transform into a greater melting point gel form.16. The method according to claim 1, further comprising the step ofmodifying the density of the liquid precursor composition.
 17. Themethod according to claim 16, where the density of the liquid precursorcomposition is modified via addition of a salt to the liquid precursorcomposition.
 18. The method according to claim 1, where the metal saltis selected from the group consisting of: zinc bromide, calcium chloridedihydrate, calcium chloride hexahydrate, sodium bromide, calciumbromide, and combinations thereof.
 19. The method according to claim 18,where the metal salt comprises sodium bromide.
 20. The method accordingto claim 1, where the hydrocarbon-bearing reservoir comprises sandstone.